brakes! Its the brakes!
I have the same problem, the calipers are sticking..
That's why I am replacing my brakes, and using brake cleaner to clean my calipers..
They just need cleaning. Buy some brake cleaner, get some lube, and do it yourself.. takes about an hour or two depending on how good you are.
The brakes stick, you drive, the rotors (not being perfectly alligned) cause the pads to "push" away from the rotors, and the sound you hear is the pads "releasing"..