My father taught me to have my thumb on the right side pointing forward. He got bolt bite or pinched or jammed or something when he was young. I do it both ways. I can't tell much difference either way.
About the sound of racking a shotgun scaring a bad guy? I don't think that it's a good tactic, but if I'm walking around in a strange place and I hear that sound, It will surely get my attention. BTW mine is nearby with one in the chamber.