Sorry to resurrect this but I'm having similar problem. It's managable for me but worrying.
When I watch anything with Win7s media player, sometimes the video freezes for a moment and then the HDD starts whirring and catches up like it FFwd'd. IT's the same HDD and I did as sturm said. There was no pio mode option in device manager, only a tick box to enable DMA. Wherever possible it was already ticked.
Is this a dodgy line of HDD's or?