My 2004 E320 Wagon, non 4-Matic, 167,000 miles, make a slight whining sound at low speeds when accelerating, but it seems to disappear above 2k RPM. Everything with a pulley at the front of the engine, except for the crank shaft, has been replaced with OE parts over the last couple of years, including the AC Compressor, PS Pump, belt tensioner, water pump, alternator, idler. The car runs great, gets excellent MPG and I use it as my daily for a three times per week, 140 mile per day roundtrip commute. It has made this whining sound for a long while. Transmission shifts fine, and there are zero DTC's on any module. Cam chain tensioner has also been replaced (just preventative), transmission fluid has been changed in the last 20k miles, and it seems to measure correctly on the temporary dipstick following the "hot" directions. I have a "chassis ear" tool and stethoscope, but no luck tracking it down as it only seems to happen while driving (not sure about that)?

Anyone ever had a similar issue or perhaps has some ideas to consider?

Thanks!

Yup my 04 wagon does it too. It's from the climate control. Next time you hear the noise press the O button on the center of the climate control. Does the noise suddenly go away? It's the AC compressor shutting off. Somehow the compressor sends this noise through the AC pipes and into the dash. The noise varies in pitch with RPM and only goes away completely when the compressor is off. The idiotic climate control turns on the compressor every time you start the engine even if the OFF button is lit. Almost all 04s (sedans and wagons) have this problem.

TJTS... I think you are on to something here. My climate control is usually on, so I've never really made the connection. As I stated, I even have a "new" rebuilt AC compressor purchased from the MB dealer, and it still makes the noise. This morning I left the climate control in the off position the entire way to the office, and the noise seems to be gone. We shall see on the way home this evening.

So what do you think may be the issue? I would have blamed it on some sort of wear in the compressor, but seems to not correlate to that.

I think the fault is the pipes in the system not the compressor. They're shaped in such a way that they carry the compressor's natural resonance or vibration into the cabin. AFIK there is no fix. I've had multiple passengers comment on the noise, I respont by pressing the O button and it instantly goes away. Press the O button again and it comes back. Some people think it's caused by the fan in the cabin but the noise doesn't vary with fan speed.

Mind blowing if this is the problem. Think about how hard it is to design a low end crappy car and then think about the microscopic details that must be dealt with in an E class Mercedes.

I’m wrestling with a rough idle vibration on a Mini Cooper and after replacing literally everything, think it is a frame rail resonance. The fix might be a spring mounted mass to absorb the vibration. How crazy is that? A friend did a top level conversion with a Honda S2000 engine into an old MGBGT. When done, he had an annoying 2500rpm intake resonance at 70 mph. I designed an intake pipe resonance chamber to quiet it down. I went to a salvage yard and noticed that a five year old Nissan had three intake resonance chambers.

Dealing with resonances are a mind blowing effort and its amazing how well they are dealt with, (and an E class goes to a whole new level).

Peter

Maybe it is the "placebo effect", but the whining definitely seems quieter with the climate control turned off. With the miles I have on this, I expect some whining noises which it still seems to have, but I'm thus far convinced that this may be much of the issue. I will continue to evaluate.... J