I put in a new motor, fired it up , and I hear a clanging sound coming from driver side exhaust , sounds like a bolt fell down the exhaust pipe. I unbolted every thing and reassembled it. Still hear the clanging , when I hit the exhaust pipes on the passenger side it sounds solid no problem, but when I tap on the driver side I hear the clanging , I have looked at it and nothing seems to be hitting anything, I unbolted the exhaust and inserted magnets vacuum hoses to see if there is a nut or bolt inside and came up empty handed.I am thinking maybe the muffler has a loose baffle or something if I hit the exhaust with my hand right under the header I hear the clang. It's got me baffled no pun intended. Any ideas what this can be? Also when the car idles there's no clanging but when I rev the motor I hear the noise.Thanks K.K.