I agree, 18a on a 960kv is kind of small. Might not be a bearing thing at all but the esc's overworking themselves.
Look out your motor ratings, see how many max amps it needs at burst, then give yourself a little safety margin.
Also, it could be that the motor timing isn't right and this is making them work really hard.
Lowering prop size might help keep the temps down, too, but first check your bearings and lube them, then check your esc to motor rating. If ok with the rating, then look at motor timing. Don't know how you do this with DJI esc's but surely there is a programming guid for them somewhere.
And, yes, you need the props balanced if not already so.