I am using the APC prop, the same one that was on the SuperTigre.
The noise really sounds like hollow muffler.
I will try moving the muffler from the OS to the Tower and see if that makes a difference.
The engine only has about three tanks through it, and I did notice that it doesn't shut off as quickly as the OS. even with the throttle completely closed, I will do the silicone thing and see if that makes a difference.
Thanks for the reply.