jsolano

Help ..! Humming Sound

I was driving on the highway my 1993, 300E, and noticed a humming sound that never ended. I was thinking that it was a truck driving next to me, but when I looked around, there were no cars or trucks.
The noise comes from my car, it comes and goes. It may happen between (80 –120 km/h) or (50 mph-75mph).
What could be causing the noise?

PS: Current mileage: 72000 miles (115000 Kms)

Thanks,

bamberger_1

check the cover underneath the engine, maybe it became loose, and starts vibrating at higher speeds. Check the tires for bubbles in the side walls. Check the transmission alignment with the drive shaft. Check the flex disks of the drive shaft.

spsinha

Check your wheel bearings, they may need to be tightened or replaced. They can often cause a loud humming/roaring noise at highway speeds.

zeronero

Right now on my car I my smog pump bearing is going out and it's pretty loud. With the hood closed it sounds like a large amount of air is being forced through a small opening, like somethings blocking the fan. With the hood open the sound can be linked to the smog pump.

If you can try to locate the sound you might be surprised what's causing it.

jsolano

Still have not found what the problem is. It seems to come from the rear part of the car. I'll check the differential fluid tonight, I believe this is not the problem since I put new fluid last year, and it doesn't drip.
I took a look underneath, and how do I:
1) Check the transmission alignment with the drive shaft., and
2) Check the flex disks of the drive shaft.

What should I look for. Everything seems to be normal.
Thanks

PS: The sound may start at 70 km/h, and increase/decrease it's sound frequency as the speed goes increases/decreases. I even put it in neutral on the highway, and the noise continued.

jsolano

I finally found out that my differential needed more fluid.
Added about 400 ml of differencial fluid and the problem seems to have gone away.
Thanks to all for your suggestions.!