Need Help Trouble Shooting a Noise
 

I recently had the Crank shaft sensor and top dead sensors replaced on my 1987 3.2 911 and I had both the rear wheel bearings replaced.

When I picked up my car from the shop, I noticed immediately that there was a high frequency sounding noise emanating from the rear of the car. It almost sounds like interference in speakers but it's not. I roll the windows down and it sounds like it is coming from the outside rear, I roll the windows up and it sounds like from the rear of the car, I pop the engine hood and it kind of sounds like it's coming from inside the engine compartment. Can't seem to pinpoint it.

The sounds comes on with RPMs and winds down along with the RMPs winding down too. Best I can describe it is like a "high frequency" sound. Perhaps it is high pressure air making the noise??? Really not sure, but it is definitely new.

It is driving me nuts and the mechanic did not really know what it could be. They don't think it is a safety issue. They were going to try and trouble shoot a few things i.e disconnect the fan for a bit etc but before I take the car in to them I thought I'd have better luck here on Pelican Parts!

Thanks so much for your time and help in advance.

Regards,

Gerry

Vacuum leak maybe???

Bump - Anyone?

I'm going to take a WAG and say the sensor is rubbing the flywheel.

+1 with Milt
Right after I replaced the distributer ignition with a twin plug crank fire setup. I was convinced that my alternator bearings were going bad. It was the sensor trigger interface, not touching, but at just the "wrong" distance apart. It sounded like a mini siren. I even bought a spare alternator to take to the track with me. When I finally figured out what it was I moved the sensor away from the trigger wheel a couple of thousandths and it was much less noticeable.

Excuse my ignorance but does the flywheel spin only when I am on the gas or when the car is in motion?

The sound definitely comes on with RMPs both at idle and while driving.

Thanks so much for the ideas! Keep them coming, the noise is driving me nuts!

The flywheel spins any time the engine is turning.

I'll agree with Milt and FPB111. Dr. Bentley says there is a certain distance that both sensors need to be set from the flywheel. Sounds as if your sensor housing (or whatever it's called) is aligned too closely to the spinning flywheel.