Also, the stock flight mode does not change the throttle when you change the bank angle, so when you are banked, some of the thrust goes sideways and less goes down, so it will drop a little. CruiseControl and/or AltitudeVario (thrust modes) will correct for that if you enable them.
First rule of quadcopters (OK, maybe not first...) don't touch the transmitter trims. Set them all back where they were when you did the transmitter wizard, then use Attitude -> Settings -> RotateVirtual to make it hover without drift. If you don't know where they were, center them and re-run the tx wizard. I usually get down to about 0.2 degree increments on rotate virtual. If it is drifting forward you subtract from pitch. If it is drifting left you subtract from roll. Etc.
BLHeli is generally good (use PWMSync in GCS setup, not OneShot) and you should not hear anything different with light damping enabled.