Clink clink, think think

To Old Upper Thomson Road, 38 km. When the transmission goes "clink", it's time to think. After installation at shop #1, shop #2 says the cassette isn't loose and sells me something else to fix the shifting problem. Shop #3 agrees with me that the cassette is loose, disassembles it and puts it back. Presto. When there's something as obvious as a clink, the ears simply can't be wrong. But since the cassette feels firmly in place, the mind naturally thinks the clink is caused by something else. It's sometimes easier to solve the wrong problems than to do the right thing. Unless there's a man who, just by listening to clinks, can tell the problem is with a cog not rear derailleur alignment. He even remembers how my old cables were routed compared to the new ones ...