Without thinking too much about it, I'd expect the actual perceived noise to decrease as cabin diff increases coz there are simply less air molecules around to transmit the sound waves.
As for cracking/creaking noises, it's very likely the trim fasteners moving a bit as the fuselage expands. The B747 Classic used to creak a bit at the rear of the FEO panel so the locating pins were lubed every few hundred hours to calm the cockpit crew.