could be ball joints. they make all kinds of different noises. most of the time they make a noise going over bumps that sounds like popcorn popping. thats the most common. i've also known them to make a woosh noise that sounds like water is swishing around. i guess they could grind too. most of the time you will feel some vibration in the wheel and on the floor upon acceleration between 25 and 50 mph approximately. hope that helps.