Originally Posted by
RH Clark
........There is no rhythm to it even keeping a steady pace on the smooth track testing it.
Stay in the same gear for an extended period at the same cadence, then time the intervals to prove/disprove some harmonic condition with 1 or 2 specific chain link(s).
Edit- Or maybe your chain is too tight and an out of round chain ring & out of round cog....
Did the new cassette have a larger "biggest" cog and you didn't add length to the chain?
Elliptical chain ring?