Some weeks ago I noticed a rattling sound when I drive along rough roads as if some iron piece in the boot was loose and falling around. I took my car to the panel beaters and they found that the exhaust rubber clip at the back of the car was missing. Another one was installed but the noise persisted. On closer observation the noise seems to be coming from around the mid-point of the chasis (under). The exhaust seems very stable and incapable of such rattling noise. What could be wrong??!!