A lot of SD broadcasters also compress (more or less) so that the quiet bits are louder and the whole sound level is boosted close to the max allowed (like FM stations which compress to only a few dB total range , so you stop at a loud channel). For KPIX our local CBS affiliate who does a good job (now) of passing the network feed, they do a lousy job of matching sound levels - network feed is fine and the network commercials are loud (but no louder than the loudest program level) but when they cut in with their local stuff ("film at 11" and local commercials) it's way too loud and has me scrambling to hit the mute button. When you have and make good use of the dynamic range that DD provides you can run into problems!
The worst offender, however, seems to be the Dish demo loop which is way too quiet - if you set the volume so you can hear this well, you might blow out a speaker or a fuse if you switch directly to almost any other channel, let alone an "action" movie!
Keep a finger on the mute button
Andy