To cover the sound of fans, pumps, ballasts, etc ... get something innocuous that generates noise.
I grow in the basement ... and directly over top (on the second floor) of where my grow is ... I have placed an empty fish tank. The sound of the water pump, air pump and bubbles breaking on the surface covers any traveling sound from the grow room below.
And if anyone is ever next to the false wall in the basement and asks about the hummmmmmmmmm ... I would blame it on the fish tank above
And yes ... I said "empty" fish tank ... just water, decor and bubbles ... no fish! We have a cat ... a very, very, clever cat
We used to have fish ... but decided that this time it was not going to be a seafood buffet for our cat
Maven