Maybe it's the spoke protector. Sometimes they rub on the cassette and that could do it. Last week I replaced a broken spoke protector, and when I was done, the cassette didn't turn at all. Had to take the new spoke protector off because that wheel didn't have enough clearance for it. You'd probably get a swishing noise while coasting from a bad spoke protector, and sometimes they break and flop around and make noise all the time.