Most RC engines arn't gonna seriously effect your hearing, starting etc... A screaming Wide open throttle 2-stroke a couple of feet from you will. Be respectfull to fellow modlers, if you are adjusting your high speed needle for more than say 30 seconds, do it somewhere else than right in the pitts. Short bursts of medium/high volume are ok, but for a duration it's damaging. I'm an Audio Engineer by trade, and clients buy my ears, I seriously value them, but don't use earplugs when I'm flying unless I'm adjusting the high speed needle, or breaking in a new engine.

My .02

~Andrew