the tranny or engine is whining, almost like if it were supercharged. I can hear it loudly in the cabin.

The has 70,000 on it, with regular oil changes. I am pretty sure that it is the transmission doing the whine, would a fluid change fix something like this?

What could be causing it?

My C300 Started to do the same thing with 60000 miles on it, always had the trans serviced every 30K. Car ran perfect and trans was too. I think the whin was in fact the trans, traded the car in at 68000. Should have kept it, 2012 C250 is such a missmatchg of tiny turbo motor and a trans always in the wrong gear. 4400 LB car, tiny turbo motor, what a mistake.

I have a 5 speed transmission that has a intermittant high pitched whine that is audable in the cabin at highway speed. It did not appear during the winter months but now shows occasionally during warmer weather as it did last summer. So it could be temperature related.

The car has done 62,000 km & it was there before the 50,000 km transmission service.

The car is 3,400lb, not 4,400lb.

Try a TCU reset. In S, it's pretty spot on, and in E it's decently quick to downshift most of the time.

See stickies. It could be torque converter failure imminent. Has the transmission been serviced every 39K miles?

I found the same whine and the mechanic said it is probably the Power Sterring pump...will find out next week and let you know.

Check that it is not fron the A/C

Long Term Whine from Air Conditioning

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I have had a high pitched whine in my A/C for over two years .

Initially I thought it was from the ATM as the sound changed with gear changes but a change in engine revs is also accompanied by gear changes.

The symptoms are :-

1.Whine only occurs with A/C in service.

2. Whine stops 50 seconds after A/C is switched off.

3. Whine occurs when A/C is lightly loaded eg. a cool day & low setpoint.If the A/C is made to work the noise disappears.

4. It is intermittent with the A/C in service.

5. The whine tone changes with rpm change.

6. The system performs perfectly.

I am wondering whether there is a harmonic of some sort associated with the A/C vanes & the throttling of the gas in the compressor.

It usually stops when the car is stationary & before I have a chance to lift the bonnet & use a stethescope

I have had this same sound for about 4 months now, any ideas what it can be? Car drives fine though..

Does not seem to change with differences with the AC

My mechanic just called to say that the noise was coming from my air conditioner, either the compressor itself or the clutch. he does not do AC work so he did not know for sure, but it was not the power steering pump..good news or bad?

There is no clutch. This is a swash plate compressor.

I had the same problem with the noise through all RPM range. It can be any component on the pulley system. If the A/C is working properly then the bearings in the alternator might be bad and you will have to replace the entire alternator.
I have 45,000 on mine and have already replaced the A/C compressor and alternator. If it is the compressor it should only whine if the A/C is on. try turning off the A/C from inside the car and see if the sound is still there.
It could just be the belt tensioner

Please let us know the outcome

The problem was a bearing in the compressor. New compressor for $945 plus about $600 in labor. Worked on it all after noon and it will be done in the morning. My mechanic is doing the work.

Sorry to hear about the cost.

If it was a bearing noise I would think that it would be a constant noise when the A/C was in service. Was this the case ? .

My noise is very intermittent.

Thanks Marti. JC

the whine varied with the rpms.

Mine varies with RPM but there is no noise when the A/C was turned off.

Is this the case with yours ?

Yes, it sounds like your compressor is seized. You'll need a new one if that's the case. They are not repairable.

Absolute BS Mate

The whine was always present, AC on or off as it is belt driven. Replaced the compressor and all is fine now, very quiet...I drove over 1,500 miles with the noise so it is not a deal stopper.

Sorry to be the bearer of bad news, but if the noise stops when the compressor is not running then the problem is the compressor. I had the same issue and replaced mine. Try lubricating the belt it might help for a while. You will only know if it is really hot and the ac can't blow cool outside air

Thanks STS.

My whine occurs intermittently only when the A/C is on so its not the bearings .

Thanks .

Our cars are notorious for serp. belt pulley problems and accessories. a/c, alternator, p/s. I've replaced my p/s pump and belt tensioner already. and I can hear another pulley starting to make noise at cold start. other than that. the car runs fine. 08 c300 6 speed.


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The compressor runs all the time. All that changes when you activate the A/C is the swash plate angle that starts stroking the pistons & pressurising the refrigerant. It's certainly not a bearing issue. It could be a worn slipper pad or swash plate issue but then it would make constant noise when activated. The noise would not come & go.

JC - It works just like a rotary multi piston swash plate hydraulic pump which you would know from your background.