Missus' 2021 epure race.  I fitted a new chain and set it up like every other bike I have ever done - one finger gap between the spring adjuster and the swinging arm.  Now it has a squeak - like a dry brake squeak which seems to come from the output sprocket at the motor end.  We have both ridden it for a while but it is still there.  Brake is fine and has not been touched, not had the back wheel out.  No play in wheel bearings or gearbox output shaft as far as I can detect.

I have backed the tension off a bit and the noise has gone.

Squeak was in time with wheel rotations so it is somewhere or somehow related to that.  My guess is a wheel bearing, but there is no play at all, sound seems to come front of chain (but I know sounds like to play tricks on you).  Any one have a thought?  I will change the wheel bearings as my next move but grateful for any input.

In lieu of a mechanics' stethoscope, I've used a length of hose to track down the source of noises.  Run the bike on a stand.  Since you needed to replace the chain, it's probably time to lube the suspension pivots.

I recently noticed a squeak at the rear wheel of a modern Triumph Tiger while lubing the chain.  I could feel no drag and nothing had been changed.  It turned out to be a dry seal on the outside of a wheel bearing.  A little Teflon spray on the seal got rid of the squeak.      

Thanks guys.  I think I will change the bearings, they are very cheap (60042RS) and it is a task inside my limited abilities.  Another one on the 'round to it' list.