In certain areas like Rakkis Crossing, Diablo 3 has insane lag, even on high end systems. Normally you would think this is because of you graphic settings, but here it is a problem with the audio implementation that has existed since World of Warcraft.
So here is what you want to do:
- go into Diablo 3
- enter the Options
- on the left side of the menu click Sound
- under Hardware you will find Sound Channels
- set them to Lowest(16)
- press Apply and Accept
Now the sound seems to be a bit off in the beginning, but you will get used to that. The lag should be greatly reduced.
Have fun! :-)