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1987 930- driver's rear tocking sound

Hi all,

I recently noticed what appears to be a "tocking" type sound emanating from the rear if the car from the driver's side. The car is mostly stock with the exception of a sport muffler and has appx 90k miles. The sound is best described as:

Not a clunk or thumping
Occurs under load and disappears when clutch is depressed (coasting)
Increases as RPM increase
Not evident when coasting or decelerating
Most noticeable when engine cold and dissipates as engine warms
Most noticeable in first & second gears
Not affected by turning or redirection

Honestly, it sounds like the "tocking" sound one can make by pulling their tongue off the roof of their mouth.

I have searched CV joints and valve train noise. It has characteristics of both.

I have a pretty good audio recording that I could share via email (I can't figure out how to post it here or on YouTube).

I appreciate any insight or thoughts.

Many thanks,

Will
Old 01-20-2014, 05:07 PM
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Send to me at og.ballard at gmail.com and I will put it on youtube for you.

From the description maybe an exhaust leak, or an issue with motor mounts? Does it not do it at idle?
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Old 01-20-2014, 05:27 PM
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16Volt,

Thanks for the offer to help. I just emailed it to you.

There is no appreciable noise at idle. It occurs only when the car is in gear and the accelerator is pressed. I hear it more at lower RPM likely because the symphony drowns it out at higher RPM.

Thanks!
Old 01-20-2014, 05:38 PM
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Wow...youtube is quite possibly the stupidest site on the planet. Still working it.....
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Old 01-20-2014, 06:35 PM
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Give this a shot:

https://drive.google.com/file/d/0BxHNOH2EIT0bUE8yeFVZNDZXeFk/edit?usp=sharing
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Old 01-20-2014, 06:38 PM
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After listening to it I would suspect a CV as well.
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Old 01-20-2014, 06:46 PM
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you only hear it once per load, or is it reciprocating?

my initial gut is CV, that's that typical sound - but some of your qualifier's like "Increases as RPM increase" kinda throw me

how are the motor / trans mounts?

is the motor tin all aligned?

any recent work done?


edit: ^heh was posting simultaneous to you^ 8-)
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Last edited by krasuskyp; 01-20-2014 at 06:49 PM..
Old 01-20-2014, 06:47 PM
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16 Volt- thanks for trying to create a link to the sound bit.

Krasuskyp- the sound could be described as rotational and is not a one time event. Interesting thought on the engine tin. Something would have to be striking it to make this sound. I'm happy to email you the clip as well.

Thanks again for the interest and insight.
Old 01-21-2014, 03:58 AM
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was just trying to think of things back there that could emit that sound - figured maybe if the tin were crooked or pinched maybe you head it popping as the drivetrain flexed on / off load

I didn't watch the vid yet but your description sure sounds like CV

could also be ebrake spring let go and is knocking around in there, but that'd be more of a tink than a tock 8-)
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Paul... CT | '87 930 | '08 M3 6gang vert |
past:

| '07 S6 | '98 M3 vert | '01 M5 | '96 993 C2 cab | '05 S600 Sport - biturbo V12@Just Not Right 495rwhp / 612rwtq |
| '58 TR3A | '01 S8 | '95 S6 6gang | '88 M5 | '87 190E 2.3-16 |
Old 01-21-2014, 05:18 AM
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I appreciate the follow up thoughts. Happy to email the sound clip (M4A format off IPhone voice memo recorder).

I'll let everyone know how it turns out.

Thanks!
Old 01-21-2014, 05:45 AM
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as RPM's increase, speed increases increasing how fast the sound is.

underload i was thinking CV.
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Old 01-21-2014, 06:41 AM
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CV makes sense in a lot of ways. My only concern is that the noise disappears when operating temp is hit. Does that coincide with a bum CV?

Thanks!
Old 01-21-2014, 08:37 AM
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Is it speed dependant? or rpm dependant?
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Old 01-21-2014, 08:53 AM
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If the engine is rev'd with no load, there is no sound. If I am driving in second gear at say 3500 rpm I would hear it with a cold engine. If, in that case, I were to depress the clutch and keep revs at 3500 RPM, the noise would vanish.

Not sure I know of a way to put a load on the engine with the CV isolated (taken out of the equation).

Thanks
Old 01-21-2014, 08:57 AM
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does it sound the same in 1st gear at 3500 rpm as it does in 2nd at 3500? if not then something to do with the drive train. if identical then it's engine related.
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88 turbo Guards red Targa slant nose, and yes I am a horsepower junkie, 3.4liter,7.5 to 1 JE pistons, Adjustable WUR, Imagine fuel head, 1 bar waste gate headers,allthe cis toys. Now apart to become the next EFI monster. fabbing my own intake, headers Individual throttle bodies, MS-3, pauter rods, Xtreme twin plugged heads, gt-2 evo cams cop's.
05 Cayenne S lapis blue
Old 01-21-2014, 10:33 AM
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My tocking sound i isolated like that ended up being a bad rear wheel bearing.
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88 turbo Guards red Targa slant nose, and yes I am a horsepower junkie, 3.4liter,7.5 to 1 JE pistons, Adjustable WUR, Imagine fuel head, 1 bar waste gate headers,allthe cis toys. Now apart to become the next EFI monster. fabbing my own intake, headers Individual throttle bodies, MS-3, pauter rods, Xtreme twin plugged heads, gt-2 evo cams cop's.
05 Cayenne S lapis blue
Old 01-21-2014, 10:35 AM
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If it follows RPM (not speed), is louder on throttle and gets quieter when engine heats up then you probably have exhaust leak on some cylinder.

Header/head flange is usual culprit (bolts break or strip out), worst case scenario is broken stud.
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Thank you for your time,
Old 01-21-2014, 03:08 PM
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Agree, sounds like exhaust to me.
Old 01-21-2014, 04:45 PM
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So, you all got me thinking…looking through the maintenance records of the PO, I saw work done in 2008 described as "weld cracks in exhaust manifold…customer MUST be aware that this is a temporary fix…We expect them to crack again in the future at some point…"

The future is now.…

Thanks again for all the responses
Old 01-21-2014, 05:57 PM
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I shoulda listened to the vid first

def not CV tock 8-)

jah, could be mani leak - would explain why goes away once up to temp

dunno tho, that sounds kinda thackety... does seem to go away once on boost, but it sorta sounds like it could be maybe valve train related too?

tough one

mani leaks should be easy enough for you to view - actually - feel & see & hear... use your senses (no not the Force, or the Schwartz either for that matter) and you'll triangulate it if there is one
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past:

| '07 S6 | '98 M3 vert | '01 M5 | '96 993 C2 cab | '05 S600 Sport - biturbo V12@Just Not Right 495rwhp / 612rwtq |
| '58 TR3A | '01 S8 | '95 S6 6gang | '88 M5 | '87 190E 2.3-16 |
Old 01-21-2014, 06:13 PM
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