I have a few basses where the knobs "dip" slightly when rotated around the pot. I'm not sure what's causing this as the knobs in each case seem to be sized properly. On one of the basses, it's the upper concentric knobs on an Audere jazz plate style preamp that rotate unevenly. For some reason this is a big pet peeve of mine, even though functionally it doesn't really matter. Any suggestions on how to fix this? Or how to measure/match up pots and knobs more precisely? Thanks!