After recently changing my bike's entire transmission, I noticed that when on the smallest sprocket, the chain is rubbing against the rear derailleur (right next to where the derailleur is attached to the frame). My mechanic tried to slowly push it outwards a bit (the derailleur), telling me it probably got bent during some mechanical shock. I accepted it as it was, although I never hit the bike and I'm always careful, regardless if I'm on the street or in the woods, trailing. Still, even after moving the derailleur towards the exterior, the chain is still rubbing against the derailleur, when on the smallest sprocket. I've done some research and my rear hub seems to only be compatible with 8-9-10 speed cassettes (it's a Shimano Tourney TX-505). Do I have to change my rear hub? Conversely, while pedaling, there's a constant sound coming from the rear hub/cassette (simillar to the sound the ratchets make when not pedaling but of a different pitch). It's there regardless of which speed / combination I'm using but it's different in intensity (louder on some speeds while more subdued on others). Can this also be caused by the hub's (in)compatibility with an 11-speed drivetrain? The chain, derailleurs, crankset and shifters are all 3x11 speed.
Edit: Some photos have been uploaded here.