Can't fix bike noise
 

Hi there guys, so i was on a night ride with my friends, everything was okay, gears where going up and down smoothly until my chain fall from the big cog, i've set the ''L'' limit screw and everything was okay, until a weird sound started, it is from the rear derailleur, but it feels more in the pedals than in the derailleur, so i took the chain off and it wasn't the pedals, tension is right, at first i taught it was the cable, but i took it off and still, the sound was there, i couldn't get rid of it, when i go in the highest gears (small cogs) the sound disappears, i cleaned and lubed my chain, still, nothing. I don't want to change the derailleur, it's a shimano deore XT m750 (I know it's old), and i really like it. The limit screws are right, it's not the b-screw. I don't know what to do, please help me guys. Thank You.

So, you don't have a creak?

Most likely causes:

1. left crankarm to spindle interface. Use a torque-wrench to install
2. bottom-bracket cup to shell has large clearances. Use teflon-tape to fill

This kind of thing is usually the cassette lockring not being tight enough.