Whirring noise during acceleration
 

My 300SD has a 'whirring' noise (fairly low pitched) while I press on the pedal. It changes pitch as the RPM's go higher. The 300SD sounds like a jet engine (or race car) when I'm accelerating. If I let off the gas at all, the noise immediately stops, irrelevant of RPM's or driving speed. It almost seems like whatever this noise is, it's coming from the vicinity of the torque converter.

Is this indicative of a problem? Perhaps time to change transmission filter/fluid?

Or is this an indication of something in the transmission or engine worn out?

The whirring noise on the car actually sounds kinda cool. My 300TD wagon sounds differently (more like a rattling tank than a jet engine), so I'm not sure if there's an issue.

Could it be your wheel bearings?

Sounds like the turbo kicking in.

If you can duplicate the noise with the Car not moving listen around with a Mechanics Stethoscope of something else like a Broomstick or large Screwdriver. Watch out for hot or moving parts.

Turns out I have the same sound on my 300TD wagon, except all the other noise (rattling/vibration of various items, door air leaks, etc) somewhat hides it. Probably the normal sound of the torque converter.

The transmissions on these cars always make a little bit of a whining/whirling sound under throttle at lower speeds.

Check that the U-shaped tube from your air cleaner into your turbo inlet is seated properly. It could also be that your turbocharger is simply making noise. That is a sign of wear but in my experience on these cars it means very little (will continue working fine for years).

Are you sure it's coming from under the hood?

Seems to me there are three reasons for "whirring" noises. One, the torque converter kicking in during acceration, and as pointed out, if the rubber gasket on that U-Tubed air induction from the below the air cleaner housing to the turbo is gone, you'll hear it louder than usual, because it will be undampered while sucking air directly from the sides, instead of through the air cleaner.

2. The other reason, would be the torque converter on the tranny, and

3. (but is more annoying and can be heard over the radio) is a bad speedo cable.

Not to mention the howling that can be heard from bad bearings, etc.

First, identify from when the "whiiring" came . . . if under the hood, then look for the turbo air induction tube. If it seems to move around the dash area, without rhyme or reason, then it's the speedo cable (plus is closer to growl). If from the middle of the car/under your butt, then might be the torque convertor. You might be due to adjust your vacuum adjustment for changing gears. That is located in the box on top of your valve cover. There are probably threads for checking that out .. . . diag and adjustments for the vacuum adjustments on the tranny.

It only happens when the car is accelerating. Revving the engine in park doesn't cause the noise (so not the air filter housing U-tube). Only when moving and gaining speed, so I would suspect torque converter?

The turbo doesn't kick in by acceleration alone. It needs weight against it, so, it's not gonna kick on until you're in motion and you accelerate.

The torque converter also may be spinning, but won't kick in to work, using the hydraulics to change gear, unless it's in motion also.

I suggest you put your head under the front hood of the car, and manually accelerate the engine, and see if you can narrow down where the sound is coming from.

sound only when accelerating in low gear? any chance it's from the diff?