Need help to ID a drivetrain related noise

[RarlyL8]

I purchased this car (2001 996 Tip) a few years ago with 87K miles on for R&D purposes to test exhaust components. It had a drivetrain noise that appeared at exactly 48mph and would go away by 50mph or so. It was a howling noise indicative of a bearing or such.
First thing done was replace the tires/wheels. No change.
We removed and replaced both rear bearings, no change.
Then moved to the differential. Changed the lube, no difference.
So then we removed and inspected the R&P, saw nothing wrong and no wear.



With all that checked out we moved to the transaxle and changed that fluid. No difference.



The option left was a bad tranny. So we bought a used one from a wrecked car and swapped it out.



You guessed it, no change.

So I threw my hands in the air and decided I'd just drive the dam thing until something lets loose, then by god I'll know what the problem is!
Well here we are 2+ years and several thousand miles later and no change!
I even drove the car one spring 1000 miles from AL to way up north and got caught in a snow storm!



Same deal, howls at 48-50mph, no other time.

I've really enjoyed the car and would like to get another one but with a manual trans, I just don't like the automatic which I bought so my wife could drive it. She doesn't drive it. Anyway I don't want to sell it with this rotten noise.
Here is the best detail I can give:
> Noise is louder when the weather is hot. Quiet in the wintertime.
> Noise is most loud in 4th gear, shift to 5th and not so loud.
> Does not do it all of the time but most of the time.
> Hit the throttle hard and shift through the gears and it acts perfect. No noise, no nothing but crisp strong shifts.
> Shift manually while slowly accelerating and it sounds the worst at 48-50mph.

So I'm stumped. This is my first 996 and I know zero about them. I'm an air cooled guy and know quite a bit about those cars.
Anybody have any idea what this could be?

[BYprodriver]

Best easy way to locate noise is to drive late at night when it's quiet next to a wall that will bounce the sound off the wall to your ears. You will be amazed at the difference.

[porschyard]

Originally Posted by BYprodriver

Best easy way to locate noise is to drive late at night when it's quiet next to a wall that will bounce the sound off the wall to your ears. You will be amazed at the difference.

Hey Brian, I guess you could try that method (i have done it myself many years ago) but my advice would be to buy or borrow one of these. It's called a Chassis Ear and I have had this tool for going on twenty + years and not only has it saved me ton's of time and misdiagnosis by pinpointing a noise location but has also proven me WRONG in my initial opinion of many different types of noises.

I wont even go in to how many squeaks, rattle's' clunk's, growl's, moan's, OK you get the picture. I have used it on every type of vehicle you can imagine. I used it on a O-540 Lycoming airboat engine to pinpoint the exact cylinder that was making noise. Have you ever heard how loud an airboat is ?

The last time i used it on a neighbor's F350 superduty he initially stopped by one evening and asked if i would go for a ride and listen to this noise, it was obvious as soon as we got up a little speed it was a frt wheel brg. and i gave it the old swerve technique left to right to load and unload the brgs and listen to the change in sound.

I told him he had a bad R.F brg. and he asked me if i would take care of it and being the good neighbor i am i said yes no problem. Having been down this road before i said let me throw the chassis ear on it before i start tearing in to it and guess what, it was not the brg i said it was it was the L.S.

I have to warn you though if you use this tool you will hear things you have never heard and wonder how some of the components you listen too ( especially Engine and transmissions) Dont blow up or explode LOL.

It has 4 sensors and 4 channels and you can switch back and forth on the fly and listen to any component via the speaker or the earbuds. I have always found the speaker kinda unreliable due to cabin noise but the earbuds work great to block out everything but the sensor noise. Compared to what you have spent so far on this car i think you would be very happy with this tool ( not expensive) and find many use's for it, not just automotive. This tool will not fix your noise but you should be able to pinpoint where it is coming from.

Richard

[RarlyL8]

Interesting idea! I'll have to go on line and see how you use one of these things.
Yes I spent a lot of money going down this rabbit hole. What I'm beginning to believe is that the tranny I installed has the same problem as the one it replaced. Stranger things have happened. Even more odd is that this noise has been going on for at least 7 years! The PO said it made this noise from the first day he owned it. It doesn't seem to get any worse with age. If it is the tranny then I'll just have to sell it as-is rather than lose a lot more money that cannot be recouped when the car sells.

[yelcab1]

I got to get me one of these ...

Where?

[porschyard]

Originally Posted by yelcab1

I got to get me one of these ...

Where?

There are plenty of videos online to get an idea of how they work. Just google Chassis Ear and multiple sights come up for videos and vendors. I rank this tool right up there with my smoke machine for accurate and timely diagnosis.

Richard