Hello Red Kite, I am not a mechanic but I had similar issue when I changed cassettes on my trainer. It wound up that when I removed the first cassette there was a very thin washer that stuck to it. I developed the noise when I switched the cassettes . After lots of time invested I saw the washer and placed it on the new cassette and it resolved the problem. This may not be the case with you But it fixed my noise. I hope it fixes yours.