Isuzu trooper grind?

Hi all, Im hoping someone out there might be able to help me. I just bought a 99 trooper and it has a weird grind going on. When I drive it with the window down I can hear a grinding coming for the back left side. It happens when i stop and when i start moving again with my foot off of the pedal. if im going 5mph it grinds on off on off and faster and faster as i accelerate. and vice versa when i slow down. but when i really hammer on the brakes it doesnt grind like a normal car with worn brakes would( the pedal doesnt bounce around either). if this sounds like something you've dealt with please write back im very greatful. thanks a lot dakota