W124 M104 whiiiiiiiiiiiiiiine
 

I've got an engine-based whine that starts dead-on 2000rpm and continues to around just under 3000rpm, which equates to 55-60mph in 4th gear. If I let the revs drop off to under 2000 it disappears. Isn't there if I slip into neutral at 60mph, so rev/engine speed dependant. Cruising at 70mph, at 3000prm, all is quiet again.

I've had the belt off and checked all accessories/pulleys etc, nothing untoward, tensioner, alternator idler & fan pulley bracket all recent replacements (noise was there before all of these done), air/smog pump is removed.

Engine runs fine, no noise at idle, power good etc. Just that annoying whine.

The only thing I've read about that changes on the M104 at 2K is the VVT system, which is engaged at 2000rpm apparently- could that be noisy?

Did someone secretly install a supercharger for you?

well, it does go like a rocket... :)

W124 M104 whiiiiiiiiiiiiiiine
 

Problem solved! You're welcome! Lol

What is the source of the whine?

If it's coming thru the radio speakers, that can happen if the alternator is failing.

Jim

VVT won't make any noise.

It might be a transmission torque converter failing, the can whistle but that is usually over a wider RPM range.

Will it make noise in all gears? If you have it in drive, foot brake on and bring the motor to 2,000 ,( torque converter stall test ) will it make noise?

I had a whine on my 1994 104 wagon , turned out to be the driveshaft center support bearing

Thanks for the replies so far, alternator is new, and it did it before replacement too.

Forgot to say also does it in neutral if the engine is revved to 2000rpm...

Since it will make noise in neutral, remove the drive belts and listen for the noise.

Also listen under the car in the trans area.

My whine in the E300d was exactly what I thought it was: cooling fan clutch. It let go while the mechanic was test driving it the other day. ....

Had a horrible squeal on my 560SEL that turned out to be the distributor bearings

Still got it, I've made a sound recording if anyone fancies a listen- the noise comes in after about 5 secs, that's as I go over 2000rpm...

https://soundcloud.com/user-468757519/whiiiine

Did you do any of the tests I specified in posts 6 and 9?

My 94 e320 estate whines as well but it does it around 40-45mph when coasting or decel down a hill. It's actually more of a whirring noise like the jetsons if anything, really only does it first time out in the morning, so I forget about it after the first few miles. I feel like it's coming from the transmission..

Just an update in case anyone is reading this in the future- the whine turned out to be the viscous fan coupling. It was a Chinese made one fitted by a previous owner. Fitted a genuine BEHR and all is quiet again! :)