I believe that sound you hear is not from the muffler, but from the diverter valve (DV) what that does is divert or recycle excess air pressure. This sound is normal. Read all about it (and then some) here:jamesbond said:I just got my gti 2 days ago. is it normal to have rumbling sound from the muffler when the gear change to first and second gear on dsg transmission. because I never drove turbo cars before. anybody?