Thanks for all the comments!

As for the creaking - we pulled the cargo security cover out the day we took delivery, so it's not that. I'll let you guys know what the dealer says - we can repro it pretty easily, but I'm not confident the dealer will have a solution.

I futzed with the speed sensing settings for the radio, but that didn't solve anything. It really seems like a "loose wire" to one of the amps.