Throw out bearing rattle misubishi GS\04

Souds comes from drive side centerline of car almost as though it coming from drivers side tire dut I think trans, when you take off it seems as though something is rattling around in the trans. The car shifts and pulls well, when you go thru the gears on the highway it goes away but when you decelrate the ugly rattliong noise comes back. Would it be the clutch disc spring(throw out bearing rattle), by any means its getting a lil' worse