Need more info (and for others the info below is helpful for most issues)
- When did the problem start - sudden or gradual onset?
- Was there an incident or repair procedure just prior to the onset?
- How old is the bike or components
- What exact procedures have you tried and what source are you using for guidance? "Fiddling" does not count as a procedure!
- For drive train problems what is the front/rear combo in which the problem does or does not occur? (use small/middle/large in front and tooth count, in the rear 3rd smallest, largest, etc. and tooth count - not 1st gear, low gear, etc.