Audio problem with HT help: volume differences from scene to scene

[evnash]

setup:
PS3 - HDMI - Sony STR-DH720 7.2 receiver - Polk C2S, 70s, Owm3, Bic 12

The problem is that ive noticed big differences in volume during movies. for example there will be a some dialog going on the overall volume would be at my normal level, well then an action scene would come up and i would notice a signification decrease in volume. enough for my wife to ask about it.

i checked the receiver and its isnt overly hot.

noticed it in man of steel last night. also noticed it during the bear fight at the end of the movie Brave. i backed the movie up and sure enough, volume degrease at the same point.

so is this just the audio mix of the movie? or could the sony receiver not be able to keep up with action scenes?

thanks