Its an intermittent sound. Initially, it sounded like the exhaust was leaking. However, upon further observation, it seems like its coming from the TC. I'm not sure if I'm giving the right description, but it sounds like a pumping sound(like, tat-tat-tat, high frequency of pumping). Definitely NOT rattling, like metal on metal. Sound comes initially with a soft hissing sound, very slight. Then after that comes the pumping sound. Happens only within a specific engine speed range and only when pickup from low speed. Went to an independent workshop, they did not know where the sound came from. Went to the dealers, they too could not detemine the cause of the sound. The only reply was that the sound is not very obvious to them. But its damn obvious to me. Danm frustrated about this,been having this problem for 3 years. Could anyone out there at least describe to me the possible noises generated by the TC??? Really desperate.....any help appreciated.Thanks.