Use lots of screws when attaching the drywall to the channel. I used one every 6 inches and still had to add more later for a few random rattles.
Trevor, I think this is going to be a multi post reply ... On this
I agree with you with a few thoughts and observations.
Going with 3 layers. The first layer goes up with a screw every foot. The next layer with a screws offset by 6”. The finial layer with screws offset 3” from that. I guess if you really wanted to be sure you could put a in one more round into that finial layer if you felt it was needed screws every 6”. That would result in a screw going into the channel every 3”.
As you probably know … each layer should be put in with a different length screw long enough to get a good grip but short enough not to exceed the depth of the channel. Now even though the builder assured me he had experience with hat channel he made a face when I asked if he was doing that. So, I made sure that he had these lengths on were hand. Unfortunately that didn’t stop the workers from occasionally using a length that was too long and as result I found a couple of shorts. I also had several rattles in different places. I’ll say more on this and your other comments in another post.
