+1 on the standard parts needing regular tightening, especially if there is the odd hamfisted wheelie landing going on

1st sign is the clunk under heavy breaking.
What I also found was that it is important to set the std cup & cone bearings to a tigher preload torque [see Haynes manual], just taking up all the slack like a taper roller setting is not enough.
I have just taken out my standard brgs and replaced with the taper kit that Wemoto sell. The standard brgs were very slightly knotchy when fully preloaded, and after cleaning them up I see the cones were slightly brinelled, have to wait for the weather to get better before I try and see if there is an improvement.