3.2L noise at one throttle position
 

OK here is a challenge.
My 1986 3.2L Carrera, very stock machine, developed a noise that I am trying to track down. At about 2200RPM, at a throttle position that I can reproduce with my foot pressure, I get a high pitched but faint electronic noise that is about 3500Hz (3.5kHz) according to my calibrated ears.

I thought it was coming from the DME under the passenger seat, but passengers (RH drive car) tell me it is the rear of the car.

Any ideas what this might be, given that it is a fixed frequency? I am guessing it is a modulation frequency used to drive injectors perhaps. Then, why am I hearing it? Perhaps a faulty connection somewhere that makes it work hard?

Another clue is that the car seems to hesitate a bit when this happens, as if an injector is not opening (thus the electronic drive working hard).

Now the trick is that I cannot hear this or reproduce it with the car static, and driving it while checking under the rear lid is a bit tricky :rolleyes: for anyone who has tried.

My mechanic has told me I am hearing things.......but it is real. Passengers can hear it when I regulate the throttle and reproduce it.

Thanks in advance. ;)
Geoff

I believe the idle stabilzer valve could produce a noise like that. Not sure it should be doing it at speed though. But if it was it might explain the hesitation. Unplug the electrical connector for the valve and drive the car to see if the sound goes away. If the stabilzer valve is the source of the noise first check your idle switch (left backside of the throttle body) to make sure it is functioning correctly. Of course I would think you should be able reproduce this with the car static though... but its worth a try.

or this...

http://forums.pelicanparts.com/porsche-911-technical-forum/322393-engine-bay-buzzing-noise-5.html

which coincidentally just today returned to the forum after a long interval:)