check your motormounts if you think it's loose. if ya not sure, then post pics of em.
otherwise do a basic tune-up (sparkplugs, wires, airfilter, oilchange, ect.) and oudda help. if it still exists after that, then it's something bigger. but a basic tuneup is always recommended with any new (old) car. it may just be getting a lack of something witch is a fairly easy fix