I have been working on and driving 914s for some years.
The only time I heard the R&P sing in decel or accel mode was when the R&P was not shimmed correctly. This rarely happens on a NON REBUILT 901.
It usually happens AFTER someone has rebuilt the 901 and didn't know how, or didn't have the right pinion setting tool and gasket thickness setup to preload the 901 R&P correctly.
Therefore after a short period of time, they start to sing in decel mode then later, in accel mode.
Sometimes the noise happens a few miles after rebuild. Sometimes after 5K miles or more.
If by chance this is the case. The R&P is a throw away item. Because the incorrect gear mesh is now imprinted on the gears and typically they will never mesh correctly even if setup by a pro. They will start to sing again prematurely.
By the way. In the U.S.
"IF" you could find a used factory 901 R&P setup tool.
It would cost ya about ten thousand dollars USD last time I checked.
I only know of two guys that have the Porsche factory transaxle tool kit for the 901.
The noise could also be coming out of the intermediate plate bearings.
Either one of those would be my first guess.
You may want to go over to
www.914club.com and look in the
http://www.914club.com/bbs2/index.php?showforum=2 forums and ask the same question (register first. It's free.) (If asked for a car vin # Just make one up. We don't care)
There's a fella over there named Dr.Evil that will have the answer for ya. You can PM him if needed.
Also look for Brad Roberts and Capt Krusty. All three of these men will also be able to answer you better than I as they both have more experiance than I on the 901. I have only rebuilt a couple of them.
Tell em Clayton sent ya over to say hello and check in with them.
The above is just my experiance. Yours may be differant.
Regards,
Clayton