Engine or Transmission Knock?

[Anthonyb]

Hello. My first post. I have a 1996 C2 Tiptroniuc with 78k miles on the clock. Very well maintained.

There is a sound that is annoying and that I cannot get to the bottom of. The car has been on ramps and had three or four different porsche engineers look or rather listen to it.

The noise occurs:

When the engine is warm
The car is in a driven gear (if it occurs in neutral, it is very, very quiet. I sometimes think or imagine i can hear it).

The noise is a deep knocking that rises with engine speed but goes away at about 1,200 rpm.

The closest example i have found online to any car that sounds even vaguely similar is on the attached link.

https://m.youtube.com/watch?v=LaZoW3SviYE

Clearly the car is older and a manual but it does sound like the noise hear.

We have used stethoscopes, removed plugs and listened from all sorts of angles etc. Best we can come up with when car on ramps is it appears to come from the bell housing area. An old school guy thought maybe input shaft?

Anyway thought of getting engine out and rebuilt but what if it is not the problem, an expensive way to fix something simple?

Have you guys any experience or thoughts or where to look as it baffles me and pisses me off when i go out in the car - which is not as often as i would like.

Many Thanks

[aigel]

It occurs with crank rpm?
How is the oil pressure?

I can't see how an engine knock would go away in neutral vs. in gear unless the trans pushes against the crank, changing something in the bottom end. (This is the case in old school torque converter transmissions, but have no clue how tips work).

What I am saying is, that I would look into the transmission further before ripping into the engine.

Also, hate to say it, but sometimes it is best to drive the cobwebs out of it and see if and how it gets worse!

G

[gduke2010]

Maybe trips are just noisy transmissions. Listend to the youtube video and the noise sounded like it was coming from the exhaust. If you had 3 Porsche experts listen to it, and they couldn't pin-point the noise, maybe the only thing wrong is the annoying noise. I know some transmissions are noisy.