Quick update for everyone.
Turns out the venting adapter that I bought from a Hayward dealer was the incorrect size. I ordered the right SKU number and part, but the wrong size adapter was shipped (without me knowing). The hole in the adapter is only 4", when it needs to be 6". That reduced size caused a backup of gasses and would cause the shaking and rumbling. Hayward is sending me a replace 6" insert. I'm assuming this is the issue, and all will be fixed. I will update everyone when it arrives (next week).
Thanks again for all the help. This forum is a wonderful resource for help!
Turns out the venting adapter that I bought from a Hayward dealer was the incorrect size. I ordered the right SKU number and part, but the wrong size adapter was shipped (without me knowing). The hole in the adapter is only 4", when it needs to be 6". That reduced size caused a backup of gasses and would cause the shaking and rumbling. Hayward is sending me a replace 6" insert. I'm assuming this is the issue, and all will be fixed. I will update everyone when it arrives (next week).
Thanks again for all the help. This forum is a wonderful resource for help!