Off my head, wow, why would you want to silence the sound.

You are right, loud sound & smoke from the exhaust are not allowed. If the vehicle came out of the Showroom in Qatar, there should be no problem. Best way would be to take the vehicle to Q-Tech or any of the vehicle checking shops on the Salwa road and they would be better able to advise. - This would be possible after Monday when eid holidays end.

Sorry, can't comment more than that.