Here's my idea of it and it goes with the loud pipes. Also the reason I put a straight cut gear timing set in my old camaro. The louder the engine is the less rattles and squeeks ya hear from the vehicle
but back on topic my 1650 was extreamly quiet. But my 1250 had more rattles and clanks then a unbalanced washing machine. Make sure your driveshaft is nice and straight and check the rag joints. Also the little bushing on the engine that holds the driveshaft. My 1250 had that bushingpop out and then it really made some noises