I recently purchased a house w/ a subpump that runs very frequently. The pump seems to work good, but when the pump is done pumping, it seems to make a “thud” (only once and for only about a second) noise that seems to be pretty loud. Is it the check valve? Or is there something wrong w/ the subpump. I wondering if I should sound insulate the pipes and subpump area to make it quiter for the room right about the subpump.