It is not the balance of clothes in machine. The tub makes banging sound when in the spin cycle. Can I adjust the balance somehow?

Under the top of the cover on washing machine there are some springs that help hold the tub balanced. This may be your problem, pretty easy fix. If you don't know, place a flat tip screwdriver under each corner of front of washer top and release locks, then lift to access these springs. Other than that it could be wtr pump, transmission or even belt.