puchak

Here is what I’ve diagnosed and how it came to be.

I had the car idling a long time ago waiting to pick up my brother, after sitting for a while it let out this loud whine. It sounded hydraulic like, I didn’t think it was me then I moved the car and noticed that it was indeed me after I turned the car off. I turned it back on, drove a little bit around the block, then thought maybe it was nothing as no errors on the dash came up. I sat idle again, and it returned but then stopped. Now the problem is different but it makes the same whine.

If the engine goes to 4,000RPM, then I let off the gas, it creates this whine for perhaps 1,000RPM then drones/whines off quietly from its peak. It sounds directly connected to it. I can also recreate it while driving, if I am at 40 MPH then suddenly brake or slow down to 30 MPH somewhat quickly, it will make this droning/whining noise then trail off at 30 MPH.

What the hell is going on? My mechanic has no idea and claims the tranny will just need to be replaced in the future. It is a 1998 C43 AMG with 45k miles on it.

ECTurboGSX

Is it possibly tied to when the engine cooling fan clutches on? Would make sense that when you're sitting for a while, the fan is going to kick on to keep things cool.

puchak

I know what the fans sound like, they’re definitely not the fans. When the sound happened it sounded really bad, something I’ve never heard since I’ve had the car since 32k miles.

Edit: I see what you mean actually, the fan clutch… maybe. I’m going to look into that.

DRBC43AMG

Have you checked for any codes? This could point you to something possibly wrong, specially if it's in the transmission

nkctb7

This is exactly what happened with my son's '99 C43 last year. A former 25+ year Mercedes mechanic from Germany didn't know what it was as he couldn't get it to make the noise when he had it. As soon as my son brought it home, it did it again. It seemed to occur once the tranny fluid was hot. At idle it sounded like a supercharger whine and it was definitely coming from the torque converter area of the transmission. We haven't gotten around to disassembling the transmission as I had it replaced with a low mileage CL600 transmission and the noise was gone. I will see if I can locate the video clip of the noise and upload it. 👍

puchak

Wow! Your description is spot on. I was trying to recreate the sound myself, it isn’t as consistent as I thought. I suppose when I pull the car out of storage I can fiddle with it again.

I did have an issue when I purchased the car where the car was low on transmission fluid leading to some rough shifts, at some point it threw up a CEL and I had it topped up. One guy said it needed a rebuild, which I thought was crazy for 30k miles, and another said that the transmission fluid was crazy low. Some sort of rings were replaced too, I’d have to check my records. Did you have similar fluid level issues?

Sulaco

722.6 will whine if the fluid gets low. It's happened in my E55 and my C43. If it starts slipping out of gear soon, there's your culprit.

Let it idle for a good 15 minutes to bring trans up to temp and check the fluid level.