Rear suspension Problem
 

Just got a 98 A4 FWD and when im cruising i can hear something noticeably loose in the right rear wheel area, i read a lot of people having this problem but only in the front, wondering if it would be the control arm or bearing as those were but mine differs because instead of it doing it at only low speeds it does it really bad between 60-65mph. Any help?

as per my knowledge
 

The shocks or vibrations encountered by the vehicle suspension are more at the speed of 60-65 mph than at the low speed. At this speed the vibration frequency is higher so the spring acts without free length means it can not absorbed the shocks. The coil of spring clashes with each other and makes the noise.
Regarding your second query that it is from rear wheel then one possible cause is this: In front engine vehicle, the engine is located at front and its inertia force is higher so the ability of frequency absorption required in suspension at the front is higher than at the rear. So the coil spring might be designed for the low frequency absorbance at the rear as compare to the front in case of your vehicle.