I have a 1987 420 sel which had been producing a humming noise while driving after warming up. I thought it sounded like a tire going bad at first so I checked them all and found them good. Now the car makes the noise much worse at most any speed- after warming up. It will temporarily stop when applying the brakes. I have raised the wheels off the ground and rotated them and checked for any sign of abrasion or wheel bearing play and found none. The last time I drove the car I noticed a slight burning odor coming from the outside and, in looking around the car touched the rear wheels which were BOTH hot enough to fry an egg after about 10 miles of driving. At this point I also noticed (while babying it home) that the brake pedal had become somewhat "spongy". After cooling off, the noise stops and the pedal returns to normal. What's going on???
BTW- The car steers and brakes normally. It does not pull to one side, and it does not feel like anything is dragging while driving at any point.