PowerDVD and auto-volume ramping?

I'm running PowerDVD 6 with an HP dvd740 internal drive. I have a cord from the drive to my SB Live! card to enable sound when I play DVDs. I'm not sure if it happens all the time as the drive is still fairly new, but I've noticed a significant amount of what appears to be volume auto-ramping when I play movies. In other words, the sound level will be normal for a few seconds, then get a little loud for a few more, then soften lower to almost half the normal level. It seems to happen when there's overall shifts in sound in the movie: when there's a loud explosion, for example, the sound softens quite noticeably rather than just staying loud. It's especially noticeable while there's music playing because one minute it's clear and the next it's quieter.

I've checked through PowerDVD's settings and don't see any setting for auto-ramping to disable it, if that is indeed the problem. I have my audio settings on regular 2-speaker stereo as I have a basic 2-speaker setup. Does anyone know why this might be happening?

m19