As soon as my daughter got teeth on both the top and the bottom she starting grinding (it was almost a hard clicking sound) the two teeth against each other. It drove me crazy to listen to that sound...it was almost like fingernails on a chalkboard to me. She only did it for a week or so. Every time she did it, I told her not to do it. I don't know if me saying something did the trick or whether she just grew bored with it once the novelty of the new "ability" went away.
I wouldn't worry about it too much...however, if your son continues to grind his teeth, though I would check with your doctor. I don't think he can damage his teeth too badly...after all, he's going to lose them anyway. However, it might make you feel better to ask the doctor just to make sure.
Good luck with your upcoming milestone birthday and wedding!!