One other thought related to Ron's post, there is a heat shield over the ignition coils. With the shop fixing the loose plug, maybe the heat shield isn't quite tight?

While I hope this is not it, I would start here, this is the most disconcerting.

I would second the 'remove the belt' suggestion. That will remove a lot of possibilities.

Anyone had a water pump fail? Any chance it's that?

I am not a skilled mechanic, but I was a maintenance helicopter test pilot for many, many years.

For us, vibrations, ticking noises, all the cacophony of sounds from all those parts flying in close formation is key. Ounces of weight on rotor blades, tuning of vibration absorbers, torque setting on Thomas couplings all had huge impacts on how the H-60 flew...called track and balance.

Clutch engagement/disengagement, gear changes can definitely affect the noise you are hearing.

All parts vibrate and the vibration patterns and interactions change as different modes (clutch engagement) are introduced. Temperature is also a huge variable in vibration patterns and sound given thermal expansion and contraction.

Lastly, noises and vibration travel from the source and "sound" like they are coming from another area altogether.

Wish I could help more, but don't discount changes in modes affecting the noise.

Quick Sea Story.

After chasing a vibration anomaly post maintenance on an H-60, I was getting very frustrated. We actually instrument the aircraft and measure vibrations, flying at different power setting, air speeds and attitudes to get the aircraft to spec vibrations and balance. I was one flight number five when it usually took two flights to get everything dialed in, especially with a good maintenance team, which I had.

My Det Maintenance Senior Chief (who was and is a friend of mine) finally asked me if I "felt" anything different about the aircraft.

Not really.

So we decided, before flying again, to open up the aircraft and check everything one more time.

That is when we discovered that one of the maintainers did not safety wire one of the cabin vibration absorber connecting bolts after setting torque and the bolt had backed off maybe two turns.

Two turns and a 20,000lb helicopter was out of tune!

Good advice all. Later on today, I might pull the access panel behind the seats to get a look at what the belts are doing and maybe even pull off the serpentine belt. Following that, I might jack up the rear of the car (again) and poke around a little. Oh, to have a lift...

Intermediate shaft bearing. Not the bearing itself but the nut that secures it to the plate in the block. Ask me how I know ha. From your descriptions that is the exact same noise I heard, an intermittent metallic tapping as the nut slowly backed off the stud and would hit the flywheel. I only started hearing it one my way home from work. The next morning at a stoplight it sheered the nut from the stud entirely. As best as we can figure the bearing going bad allowed enough play in the assembly for the nut/stud to jiggle towards the flywheel and then wham after enough hits severed completely.

I could be wrong but
http://forums.pelicanparts.com/uploa...1378255035.jpg

We found that nut sitting in the bottom of the bellhousing after separating the engine and trans after at the previously mentioned stoplight where after it sheared the stud oil just came pouring out.

Good luck man.

So the one car that I have encountered with an IMS issue did have a mechanical sound that was similar in random occurrence but not in the sound itself. In my case the sound was a metallic "ping!" that was random and only heard on cold startup for the first 90 sec or so. It was a 2005 997 that locked up the engine about two days and 2,000 miles later.

Yikes! Judging by your signature line, that was the end of that engine, correct?

Here's the thing, though: the 987 has a totally different IMS bearing setup than the 996. I'm not sure that it has a nut or stud like that -- you have to split the case of a m97 engine to get to the IMS bearing.

When you say "locked up the engine," do you mean that that engine was toast? You don't hear about too many m97 engines that have catastrophic IMS failures, at least not compared with the m96s.

Another thought about the IMS bearing: wouldn't I see debris or at least metal flakes in my oil if this was the case? The oil sump was pulled and found clean, the oil was analyzed by Blackstone and found clean, the filter was inspected and found clean, and there was no ferrous debris on the magnetic drain plug.

Question: if a bolt on the IMS bearing was indeed backing out and slapping the flywheel, this would be possible to check by separating the gearbox from the engine, correct? In other words, far less intrusive than splitting the case?

Yeah, it was weird. The engine didn't skip a beat, didn't jump timing or anything. I remember restarting it after it stalled and it felt... crunchy. That's not how you want your engine to feel but really is the best descriptor as it ate the bearing and then it smoothed out and felt completely normal as I drove it around the block to my parking spot at work. It possibly could have been rebuilt but that was that.

You're right though, I didn't think of the differences between the 911 and the cayman anatomy when it comes to the bearing and plate. Just the way you described the noise made me think of what happened to me to a tee. Yeah, I'm no expert but that seems simple enough to check for by just splitting the engine and trans rather than cracking open the case.

I definitely wouldn't panic just yet! Check out the simple solutions, particularly as it relates to the work that was recently done. It could easily just be something loose. But if I ran out of potential solutions, I would definitely pull the transmission to inspect the bearing. Lack of metal is a great thing, because if it is the IMS that means you caught it early. It's not unheard of for there to be a sound prior to IMS failure, sometimes for weeks before. It gets called the death rattle, and is frequently compared to the sound of a marble bouncing around in a coffee can. Which perfectly described the 997 that I described. In that case I believe the car actually did lock up, it died on the highway and wouldn't turn over.

good luck

Good advice above to isolate each system, like pulling the engine belt, heat shield... stethoscope or a screw driver or long extension to various points on the engine or trans.... methodically eliminate what you can. You'll find it.

Thanks for all the input and support, guys; see, this is why Pelican is always my first stop for advice! I will be checking various things this afternoon; I'll try to take more videos and pictures if I can and post them later.

In the meantime, can anyone speak authoritatively about the differences between the m96 and m97 IMS bearing? I mean, I know that the m97 is mounted inside the case so that the case needs to be split to access/replace it, but is what LSA describing w/r/t his 996 Carrera possible in a 987/997 car? It seems as though the IMS bearing "backing out" wouldn't be possible if the IMS is mounted securely inside the case, but then there might be aspects of the design I don't understand.

Okay -- I played with running the car with the belts on and the belts off, and I can report that the nature of the noise did change somewhat, but I'm not sure that my findings are anything close to conclusive.

Start #1 -- Belts on: the noise is present.

Start #2 -- Belts off: I thought I hear a tap or two when I first started the car, but when I got underneath, everything seemed fine. No noise present.

At this point, the neighbor started mowing his lawn, so I decided to close the garage doors (with the engine off!) and inspect the belts a little:

https://www.youtube.com/watch?v=TkmAb7Xol6k

The pulleys seemed fine to me, but I'm far from an expert in the matter.

Start #3 -- Belts back on: the noise is present:

https://www.youtube.com/watch?v=xUtrr4txXiA

Start #4 -- Belts off again: the noise is gone completely:

https://www.youtube.com/watch?v=1EhXYgRFSWc

That might seem like good news, but I did THINK that I heard it the first time I took the belt off... and when I put the belt back on again after that last video, I did hear an occasional tap/tick, but very infrequent and diminished. It's possible that the car was getting to be near running temperature at that point, and as I've said, the noise doesn't seem to be present when the car is hot. SO: I think I might let the car cool down a little, take the belt off again and see whether the noise is there. I'm nervous about letting it run too long without the belts on, as I don't want to completely drain the battery.

Thoughts at this point?

Let it cool down completely and run it again without a belt. Don't worry about running the battery down that quickly, if it's fully charged it won't drain that quickly.

I have had belts make a ticking noise, but it's pretty rhythmic and not random.

JR

let cool. try again. completely confirm or eliminate the belts.

Hoping for easy stuff!:D

I'm probably totally off base and did not even listen to your videos, but FWIW my cayman S once had a failing water pump which was making all sorts of weird noises under similar conditions... Took the dealer ages to diagnose, drove me insane, they had no idea until it got really worse.. just a thought. That would be better than am IMS bearing !

UPDATE.

Let the car sit and cool an hour or so and then tried again.

Start #5 -- Belts On: There's the noise, clear as day.

Start #6 -- Belts Off: I heard literally one "clack" that was definitely the noise I was listening for, but that was it. Take a listen:

https://www.youtube.com/watch?v=6gZ8MwrBFA8

Start #7 -- Belts On: The noise is back, just as in Start #5. Take a listen:

https://www.youtube.com/watch?v=YWKjcccw8JA

The removal of the belts DEFINITELY has an effect on the nature of the noise. Although I have heard single, solitary "clacks" with the belts off, they are very sporatic and not nearly as frequent as when the belt is on, to a noticeable degree. The car definitely runs smoother with the belts on (obviously, since the lack of an alternator with the belts off means that the car literally has less power), so maybe the rhythm of the engine might be a factor here? Thoughts?

Also: I threw a CEL when I ran the car with the belt off this time. Is that normal? In other words, was it caused by running the car without a belt, or might it have been caused by whatever is causing the noise?

The CEL might be due to your battery getting low. When you run with the belts, does the tensioner ever seem to jerk or jump? Or are they smooth and consistent? Any luck localizing the area that the noise is coming from?

Water pump is an interesting potential, when they fail sometimes the bearing gets loose and the impeller contacts the block. Worst case sometimes the impeller totally disintegrates and spreads plastic through the cooling system. Did you try turning the water pump pulley by hand without belts to see if you can feel any play or internal contact? Any idea if the water pump has been replaced?

Interesting access through the rear driver compartment. With the covers off the engine, are you able to localize where the clicks are coming from any better? (For example, is it louder if you stick your face in front of the access from behind the seats?

edit- +1 pn spinning the water pump and looking for play. I'd also spin all the tensioner pulleys looking for play/smoothness/ slop while I'm in there.