Originally Posted by Gooroo
Most of the surpasses had one piece mufflers but you never know.
Nope.... two part, screwed together with very fine thread, and probably lathed down to final finish after assembly.
I found out when I tried to make cooling fins in mine, and being almost finished doing so, suddenly cut into the thread....
But that should not be the cause of this problem (if there is any.... I wonder), because I never saw those mufflers come apart. Not even mine which runs uncooled and reaches close to 400 degrees C.
Some surpasses just have a slightly knocking sound, especially when they are being run at peak power with a heavy prop, and sometimes the plane they are bolted on, act as resonating body, amplifying this sound.