Whistling sound from engine near red line.
 

I was driving to work this morning and after the car was throughly warmed up, I was excersing the Varioram ;) along a deserted stretch of road.
After the tachy goes past approx 6k rpm, there was this strange whistling noise from the engine compartment. This happened in second and third gears. Since this was definately not a routine sound, I did not risk it happening again and drove in to work at a much more sedate pace.
Has anyone experienced this before?
Could it have been from the A/C, as this was on while I was opening the varioram up?

As always, the collective wisdom of the list is much appreciated <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Check the belt sensor. It's a small wheel that presses against the belt via a tension spring. The bearing apparently dries out and the wheel whistles when turning at high speed.

This is a fairly common problem on 993's. It can drive you nuts diagnosing it, because it sounds exactly like a hihg pitched air/vacuum leak. If that's your problem, it's a cheap and easy fix to replace it.

I also hear a high pitch sound from my engine bay only when the A/C is on during full throttle high RPM accelerations.

It doesn't do it when the A/C is off, I just figured that it must be the A/C compressor pulley that's making that noise.

Just curious, though not the sound Leslie brought up, but a really faint, high-pitched whistle sound when accelerating gently...but only when on the gas. When you back off the gas, it stops, back on the gas at mild acceleration, sound comes back. Nothing weird happens. I chocked it up to the some kind of F injection noise? Anyone know the sound I'm describing?

Edward

Maybe alternator noise coming from the speakers?

I had exactly the same problem. A high pitched whine that increased in pitch as I stepped on the gas. It only happened when the radio was on. I was told that it was probably interference from the alternator. But pulling out my radio and checking that all the wires were snug fixed both this problem as well as static on my right hand side front speakers. So looks like it can also happen from loose wires connections on the radio.

I know the whine is not from the radio because the radio is off. Also, the high-pitched whine is so subtle that you only notice it WHEN the radio is off AND you're listening for it.

Alex,

If you're getting a whine only when your radio is on, that whine IS most likely from the alternator. This isn't any sort of loose connection but is interference from the alternator THROUGH the actual wiring. You may actually even hear the whine pitch up and down with the RPMs. Any competent stereo shop can eliminate this with the right value capacitor in the power line to your radio (and amp if you have one).

There must be the possibility of interference from somewhere other than the alternator as on two separate occasions in the last two weeks removing the radio and checking the connections immediately cleared up the whine I was hearing. I'm not sure what was causing the problem but my method definitely solved this problem s well as a heavy crackling on the two higher upper speakers on the passenger side door panel.
Then again my fathers first recommendation was exactly what you were mentioning about the alternator and the recommended fix.

My '97 993 coupe makes a high-pitched humming sound under full throttle starting at about 5700 RPM. While working a corner at last weekend's DE event, I heard another 993 making the exact same sound as it drove by. I wouldn't call it a whistling sound so maybe this is not the same issue you are experiencing. My sound is certainly not electrical in nature and I just had my belts replaced about 400 miles ago.

Guys,

Thanks for all the replies. I went in to the dealer at lunch to consult our resident guru. He looked at your postings about the belt sensor bearing and agreed that it would be one of two possible causes of the whistle after we went for a test drive and 'activated' the whistling a couple of times.

We drove the car back to the workshop and he pulled out a torch to look at the condition of the belt sensor. Lo and behold, the RS does not come with a belt sensor!! (Guess you learn something new everyday!)

He diagnosed that the only other source for the whistle would be the bearings in the alternator. The car will go in next week to get the bearings serviced. I will report back if the problem does not go away.

Radio silence would mean that the problem is sorted.

Once again, thanks guys for all the help <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" /> <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

I too noticed the whistling sound when I got to drive my car again! Mine is as Edward described it. As I press the gas pedal it comes and then goes. It is not a whining noise and I can hear it better with the top down. I pressumed it is the new motorsound airbox I installed as I hear lots of new sound from it. Edward do you have the motorsound cover as well???

DJF1,

I don't have the "motorbox" lid, but yes, I've carved out two large, neat rectangles in the cover. As it occurs only on mild accel, (actually, it's probably on ALL acceleration but the sound of the intake and engine mask it) it's my guess that it's some fuel injection noise....perhaps someone knows better?

Edward

Maybe its a completely different noise (its hard to 'get' someones noise from a description!), but I have something very similar happening in my 964.

When I 'cane' the accelerator and get the engine over 5000 revs I can hear a faint but consistent whistle. Its quite soft but also acute, though I am sure any passenger wouldn't even notice unless they would be listening for it.

I just put it down to being the way the car works.

Any update to this...Im hearing the same noise under accelaration at high speeds goes away only when I relase the gas pedal

I have a whistle sound at just the right light throttle inputs. I can load the motor more and it goes away. If it idles its not there. I think its coming from the throttle body area.