Vista - DVD-Drive Spins Up During Movies

When I used to watch movies in Windows XP, my DVD player would correctly spin
at 1x, so as to minimize noise / vibrations. However, when I now watch
movies on the same drive and computer in Vista Ultimate x64, the DVD
consistently spins all the way up to maximum speed, which causes an unholy
racket. So far I have determined the following:

This occurs with all movie DVDs (I've tested several different titles)
This occurs both in WMP11 and all freeware players I've tested
This occurs with different codecs (tested Cyberlink's and ffdshow)
This occurs regardless of output settings (overlay, VMR9, EVR, etc.)
This DOES NOT occur if I play a movie in Cyberlink's PowerDVD player

This is a stab in the dark, but I'd guess the problem might have to do with
Microsoft's DVD navigator filter (?); everything else seems to be ruled out.
Also, I've already updated my drive (Pioneer DVR-110D) to the latest version,
which made no difference. Finally, for various reasons I don't want to use
PowerDVD, so I'd really much rather have other programs work properly. So:
does anyone have any idea why a modern DVD drive would run at full blast
during a movie?