I tried recording a DivX to VHS and got what is probably the same problem - the picture and sound kind of 'warble'. I haven't tested yet, but I have a sneaky feeling it might be a 50 vs 60 Hz thing. Being in UK my video will be 50 Hz, but my Xbox is set to 60 Hz. I'll try setting the Xbox to 50 Hz before recording and seeing if it works - you might want to look into similar things (depending on where in the world you are).
pelago