weird "vibrating" sound... kinda choppy, maybe?
It sounds like Acid is tempo-stretching them Check the track properties to see what tempo acid thinks the track is. If this differs from the project tempo, then Acid is probably trying to adjust the sample to fit the tempo.
There's a number of ways to stop this... It's the default setup for loops and disc-based samples, i beliee, so for those you need to "reset" what it thinks the tempo is. You can do this in
Sound Forge, or any other editor that lets you edit "Acidized" loops. It doesn't actually change the tempo, just the tempo that the loop tells Acid it is.
-D