I've narrowed it down to the fact it occurs everytime the reusable link comes off the rear sprocket. Especially on the smaller cogs!!
Can you change it for another brand/design of link or shorten the chain slightly.
Sounds like a pain, once saw a riders chain jump on a good sized drop and he landed on his face without his helmet, his arms slowed him down a bit but he still got clobbered in the puss, with a bing 😯
Didn't help that I was hooting and laughing, also shouting if your hungry have a burger 😯 I did walk him back to the van and make sure he was OK.
Good luck sorting it!
Is it a Powerlink? Silver is 8spd and wider, if you use that on a 9spd chain it could foul the sprockets.
Check the links are not stiff either side of the powerlink. If its worse on the small sprockets, I'd put money on it being a stiff link.
Sorted thanks, went back outside in a huff after posting, main reason was I'd just spent 2 hrs stripping and rebuilding the mechs, new cable and outer and it was still jumping. Decided to just sit and watch whilst turning slowly and spot on spooky, stiff link 2 away from the joint.