Manual C4 Noisy Transaxle venting issue?

[914turboford]

My 1999 C4 makes a rattling noise while idling. It gets better when the clutch is depressed but does not completely go away. I believe the trans also makes a noise in 1st, 2nd and 3rd, but again not very noticeable. I put the car up on jackstands yesterday and ran it while underneath.

The noise while idling makes a sound like a leaking exhaust, but it is not coming from the exhaust. In fact, it seems to be coming from the top of the transaxle toward the front of the car.

I pulled the trans oil fill plug to see if it was low on oil. Very clear oil poured out, which I thought was good. While removing the plug, there was a sucking vacuum. I.e., air either escaped or entered while removing it ( I think air entered). Could there be any correlation between this and the trans sound?

My trans shifts perfectly and is supposedly (I have records) a low mileage (30K) new trans from Porsche, albeit installed 10 years ago.

This car has an aftermarket single mass flywheel and high performance clutch as well. Before purchasing the clutch supplier told me this type of flywheel will cause rattling at idle.

I tend to think the worst, that I have a bad bearing and that trans r&r is in my future.

[FPB111]

Rattle with single mass (lightweight) flywheel is known byproduct of the flywheel. Porsche uses a Dual Mass unit to dampen the gear rattle because of this.

[JFP in PA]

Originally Posted by 914turboford

My 1999 C4 makes a rattling noise while idling. It gets better when the clutch is depressed but does not completely go away. I believe the trans also makes a noise in 1st, 2nd and 3rd, but again not very noticeable. I put the car up on jackstands yesterday and ran it while underneath.

The noise while idling makes a sound like a leaking exhaust, but it is not coming from the exhaust. In fact, it seems to be coming from the top of the transaxle toward the front of the car.

I pulled the trans oil fill plug to see if it was low on oil. Very clear oil poured out, which I thought was good. While removing the plug, there was a sucking vacuum. I.e., air either escaped or entered while removing it ( I think air entered). Could there be any correlation between this and the trans sound?

My trans shifts perfectly and is supposedly (I have records) a low mileage (30K) new trans from Porsche, albeit installed 10 years ago.

This car has an aftermarket single mass flywheel and high performance clutch as well. Before purchasing the clutch supplier told me this type of flywheel will cause rattling at idle.

I tend to think the worst, that I have a bad bearing and that trans r&r is in my future.

From the factory, Porsche uses a dual mass flywheel to dampen unwanted harmonic and torsional forces, replacement of the dual mass with a single mass will cause these forces to be transmitted to the drive line.