squeaky suspension

[kenwood guy]

I notice that when im driving around town and the truck hits suddenly mild rough surfaces the there is a squeaky sound that sounds like comes from the front driverside tire however when the passenger side tire hits sudden hard surfaces the sound comes back again its really annoying anyone got an idea on what it can be?????

[wrparks]

I've noticed lots of silvy's do this once they hit about 4 years old. Not sure what it is, ours were all beat up farm trucks, so we didn't care as long as they ran.