if there is air in the lines, these pumps get loud and angry. Sometimes it takes some doing to get all the air out.
have you sucked the tank dry lately?
I even had it once with a hairline crack in one of the suction side fittings (actually the strainer cap), and it was pulling air in. It wasn't until it started leaking water after it got worse later on that i found it.
Before doing anything too drastic.... I suggest
1) giving the plumbing a good looking over for loose or cracked fittings or components....especially since work was done to it lately...
1a) while you're at it make sure the mounting screws area all tight and good
2) then letting it pump some water through for a while.. let the bathroom sink run a long while, then the shower, etc... to give it a really good purge
then see if it settles down. I'd probably start with the faucet closest to the pump and work away from it....
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