81 300SD

Replaced brake pads yesterday and drove it 10 miles or so to a party.
A slight loping sound was present but really faint.
On the way home the sound began to get louder and harder.
The sound and feel stops when I depress the brakes but not when I
coast.
The pad replace went without incident it seems.

Anyone know what it could be?
The tires are new and fine. I cannot even think what would be making the sound. I figure if the sound started after the brake job and stops when the brakes are depressed then the sound is brake related.

Ideas?
Thanks!

__________________
Ginny in Denver-ish
78 300SD, 265K (mine)