How can I quietly tear down drywall?
Well, you really only need to punch one or two holes in the drywall to get it started, then you can simply pull it down with your bare hands.  Assuming it's really just drywall and not something heavier.

Sawing lines won't really help, however, as properly installed drywall has screws ALL OVER it - so just go with  "punch hole and start pulling"...