Kyu Cha

Hi guys, been a member for quite some time but this is my first post. I own 2007 997 Turbo Tiptronic, currently 55000km. Car has been making a grinding noise. I have checked CV and wheel bearing (without atually removing but with stethscope) but could not find anything wrong, CV boots are intact with no leak. I also checked engine mount, transmission mount and found nothing wrong. Found driveshaft guibo worn & damaged so replaced but noise did not change. I also changed all 4 tyres to Michelin 4S but no change. I carried out front & rear diff fluid change, transmission fluid change, front diff clutch fluid change but no luck. I also tried unplugging the electrical plug to the front final drive clutch which gave PTM fault on the dash, I did test-drive short distance and the noise was still there.

This noise been there for over 5000km, been to couple of Porsche dealership and independent shops, mechanics suggested to keep driving until the noise gets worse so they can track it down easily but this did not happen. Noise never got worse. It only happens from cold until the engine oil temp rises up (for 10-15mins). Especially after I turn corner or when climbing up a hill, happens on 3rd and 4th gear., no change in neutral. Noise apparent after turning a corner, does not happen while cornering.

Today, while I was scanning the car, I went into PTM module, checking actual values, found a temp reading from front diff was -495C.
My understanding is this sensor located at the multiplate clutch of front final drive reads the fluid temperature. How can that be in negative value? Could this affect anything to make grinding noise? Went into Tiptornic module to see and temp sensor there reads 80C after a short run so normal.

I hooked up 4 wireless chassis ear under the car today, will test drive it tomorrow morning when the car is cold. But would like to hear if anyone had similar symptom or if there is any other areas should I inspect?
Uploaded an audio file although not too sure I clear it is, recorded within the vehicle while driving (from 11sec to 15sec).

Ji H. Jung

@Kyu Cha Did you solve the problem? I got same issue on my 996 Turbo, when rev reach 1800 ~ 2000 rpm in 3rd, 4th, sometimes 5th especially uphill condition (much louder)
I think slight grinding noise coming from front differential area. I still struggle with this issue. Please share any comments

Kyu Cha

Yes after 6 months of tackling the noise, we came to a conclusion it was TCU and PTM modules software being corrupt. Try disconnect the battery overnight, reconnect in the morining and test drive. If no noise, then its the module.
There is a service bulletin of this problem for 996 turbo. Also check the temperature sensor if there is one at the final drive. Mine read out -489.50 but it did not throw any code or any light on dash so may need to get in to the module's actual value reading from scanner.

Ji H. Jung

Thanks a lot, Mr. Cha
I wish it would relate module, Only different symptom between yours and mine is that mine has nothing to do with temp I guess.
I got noise when rev reaches 1800 ~2000 rpm in 4th 5th (sometimes 3rd). Anyway you suggest me to unplug a battery overnight and reconnect next day and do the test drive?
Will TCU and PTM module get re-arranged by doing this?
if yes, it could be very simple problem (I wish!!!!)