I've put up a bunch of them, and yes sometimes the walls creak (which can be freaky). When customers worried about the mount I'd take the TV down and hang from it. (I'm around 215lbs on a good day) There were very few TVs that weighed more than I did.
What size bolts did you use, and did you pre-drill pilots into the studs when the mount was installed?
Some mounts come with HUGE lag bolts and if you don't pre-drill properly they will split the studs in half. If that happened you would have heard a loud pop when the bolts were being installed. And most likely a lot of nail pops in the dry wall (Seeing the screws bulge through the drywall, although this can happen anytime with a mount if the drywall compresses when you torque down the bolts)