BR:
Cos’ you know all about me, and my understanding of Bikes / mechanical things… I didn’t used to work in a bike shop, nor am I Senior Engineer in a with a large upmarket vehicle manufacturer at their Huge Prototype Vehicle facility, looking after a team of guys building 100’s of VERY VERY expensive & COMPLICATED vehicles each year. I understand **** all!!!!
My original question was “what could be wrong with this -have you got any experience that may help?” not “help me I don’t understand how to fix my bike”
I don’t know you, and you don’t know me, so I’ll leave it at that.
What would concern me more is if I was off on a 4 week MTB trip and couldn’t fix/understand the problem…
and as ANTIQEE said to inspect and potentialy fix the problem:
and not taking a chainwhip and cassette tool / wrench