Originally Posted by
Trakhak
If you bought the bike from a local bike shop, bring it back to them to address the problem. Most if not all bike shops provide at least one free tuneup within 90 days of purchase -- and will do quick adjustments when needed for individual problems that arise within that period.
If you bought the bike used, you might be dismayed at some of the responses you're going to get here. There are a number of possible causes of that problem, many of which can't be confirmed without going to a bike shop and paying a mechanic to fix the bike.
I warned the OP! From his/her/their point of view, chances are that too much information has been forthcoming in this thread.
So:
Just take the bike to a bike store and describe the problem.
If you bought the bike from them and the bike is undamaged (e.g., you didn't crash the bike, etc.), they should be able to fix it for free.
If you didn't buy the bike from them, at least get an estimate for what the repair should cost.