1991 Toyota Supra Clicking Noise Relative to Speed

My turbo Toyota Supra has started to make a clicking/ticking noise that Increases relative to my Speed. when the car is stopped there is no ticking. i can here it when i drive close beside buildings with the car windows down. the ticks occur about every foot to 18 inches of road distance traveled. i want to restore this car when i get out of engineering college and i don't want it to bust something while i'm driving it. please help! Thank you, Sam