Insulation behind HardiBacker?

Hello, Im new to this site and have a question about my bathroom remodel. The bathroom I'm remodeling is surrounded by all interior walls (bedrooms). I am about to install a new tub and tile surround.
If I insulate the walls before I put up the cement board, will it help sound proof the bathroom? I am also worried about the moisture being trapped by the bats of insulation. I am a total newbie and need some guidence,
thanks in advance..

Insulation will help, but not stop noise transmission. You should have a vapor barrier behind the cbu, so use unfaced batts, then put some plastic up. If this is a shower, run it down over the liner. If it is a tub, run it down over the tiling flange and you should be fine.

For tiling help, check out www.johnbridge.com.