99' moan, groan or droan noise from rt rear

I searched past threads and found the term "droaning noise" from the rear that hits the nail on the head for this noise. It only lasts 2-3 seconds from a dead stop only and goes away. It's a manual so it's hard to get to the brake quick enough to see if that's it or not. It happens 3 or 4 times out of 10. From 2004 the poster said he thought it was the new set of Hawk brake pads he installed. The one reply he got was "if the brake pads are metalic, they'll make some noise". Not like this they won't, not all metalic brakes, (and most are metalic these days). If anyone else has had this noise and fixed it with different pads or proved it was the pads and not an axle bearing or something dramatic, I'd like to hear back. It's on my sons car and he's been at college since September. We changed his brake pads just before he left and just last week said it had been making this noise for a while. I don't know if "a while" is 7-8 months or not. If it started when he left for sure then I'd say leave it as long as I know that it's the pads.
Thanks in advance guys...and or gals.

Droning, to me, means an exhaust drone. Such as with after market exhaust/muffler. At certain RPM ranges, exhaust systems will "drone, where the resonance frequency is just right to make the noise very loud and annoying.

I've never heard anything else described as droning on a car. Are you able to take an audio recording of it?

It may be sticking brake calipers. Lube the slide caliper slide pins and see if that helps.