Humming noises in the back - they are noisier at lower speed than higher speed??

Question by petediegan posted 2 days 15 hours ago in 2008-____ (W204)

More humming noise at lower speed than higher speed?

I have a MBC300 2008 at 154,000 miles and it is in very good shape.  Rear right wheel bearing had been replaced 5 years ago at 96,000 miles.  Recently, I have humming noises again.  My mechanic, after replacing control arms and checking on wheels said that it is due to front wheel bearings turn bad.  Guess what?

After I had him replaced both front wheel bearings, the humming noise is almost still there!  The problem is: when I pay particular attention to the noises, the humming noises are more noisy at lower speed (20-40 mph) than they are at higher speed (50-70 mph).  That could NOT be signs of rear wheel bearings turn bad, could they? 

And if they are not from the rear wheel bearings (whether right side again or left side), where could they come from in that manner and/or nature?  Thank you for your comments and/or consultation if you could.