can anyone tell me why my '02 altima with 180k miles and a rebuilt engine make rattling noises (like a tin can) when the engine is idle and accelerating? the sound seems to appear just as it's time for an oil change. after the oil change, the sound stops and doesn't come back until about 25oo miles later. there are no oil leaks or smoke coming out the exhaust. what's going on? also, sometimes when i turn on the a/c, the same rattling noise appears. any answers/insights would be greatly appreciated.