It's common and there is really no way to fix it except complaining to the provider. In reality, since DD has a higher dynamic range there should be a difference in the output, with DD being lower. But I don't think this is the case with broadcast, because my HD volume output on cable is all over the place, changing even from commercial to commercial, never mind channel to channel.
ha ha ha ha ha ha....reminds of the (mime) Marcel Marceau album. No, he really did put out an album. Lots of quiet, scuffling sounds, then audience laughter. Priceless.