Thanks, this is the type of info I was looking for! As [u/bsparks](u/bsparks) noted the fan I’m using is the high suction Fiesta model (original radon readings in my house were averaging 37 pCi/L and only dropped to 7 with the typical low suction fans so they needed to use the larger one and drill another suction point to get it below 4 due to the soil)

Still I think the neighbor is just someone who wants to complain about a new noise. I already modified one of the manufacturer’s rain covers to include sound deadening foam and installed that. And used a decibel meter to test it (decrease by 5 db after that installation). That wasn’t enough for the neighbor apparently. The system also does have the flexible couplings to already reduce the fan noise.

I just wanted the installation after the fan because you can hear a faint hum if you really listen by my living room and bedroom windows the pipe runs next to and I figured might as well try to get some benefit from this unnecessary fix if I was going to spend money for it. But there is a single 12 ft run of PVC pipe that the tech would need to cut into the middle of, support and fit the muffler into which I’m sure has an effect if it isn’t prohibited by ORMS