HELP! Knocking noise underneath house!

[rockncountry101]

I have a new Legacy single wide mobile home. Every time the heat kicks off, a few moments later it sounds like I have people underneath the floor beating on it. The sound will transfer from the floor to the wall. After realizing that I would get no help from the factory, I hired a contactor to come out. He did discover that underneath in the same vicinity, there was a 2x6 floor joist that had a huge chunk missing. He fixed this by installing another 2x6 up against it. Since then, I have heard no noises in the floor with the exception of the ducts banging. He is going to come back out and suggested that we cut the tie straps around the duct that is connecting it to that particular joist. It connects to each joist and they are 16oc. I am loosing my mind and simply cannot deal with this anymore. Does anyone have ANY suggestions? Thanks.

[Greg]

Is it possible that it is a duct noise from the expansion/contraction due to blower pressure or heat?

Maybe it is a mouse knocking to get in, It's cold outside!!

Greg