What is that wierd noise??????

Everytime my 88 Supra slows down to like 20-30MPH during driving, it makes this irritating noise like clicking sound. Other times, it sounds like something is grinding against the wheel. I believe it's coming from the front passenger side of the wheel. I look around the are but found no loose nuts. What could it be??? Thanks

I've seen some other model cars do the exact same thing afer having the brakes serviced. A neighbor had an eagle talon she took to wal-mart or something to have her brakes serviced, and it made popping-ticking noises in set intervals as she slowed (even without hitting brake) Drove her so crazy she sold the car. Something to do with caliper or rotor too tight? Dunno, replaced my brake system almost completely (everything but lines, may have to do them too), and never figured out what they could be overtightening...