DV Info Net - Vegas 11 visual/audio synch slipping on render

Hi All,

New to Vegas and have been having some problems. When I render out files the audio and visuals sometimes slip out of synch in the finished video. This is sometimes for just a few frames or seconds before slipping back in again, and sometimes on and off throughout the video. It seems to happen regardless of whether effects are applied to parts of the sequence or not.

I have a Sandy Bridge i5 2500k, 8 gigs of ddr3 ram, windows 7 64-bit, Nvidia Gforce GTX 570

I am working with 28mbps AVCHD 1920x1080 50i footage and 48/24 wav audio files and grading with Magic Bullet.

I have tried rendering to .wmw, mp4 and AVCHD files but always come up against the same problem.

I have tried disabling GPU acceleration when rendering.

I have tried lowering the res. of the preview window.

I have tried shutting down every background task I can think of.

I'm sure I've just missed something obvious but any help would be incredibly gratefully received. I'm somewhat at my wits end.

Thank you very much,
Henry

UPDATE: disabling GPU acceleration removed most but not all of the issues. Having rechecked the source files I'm afraid that the remainder look to have been down to human error on my part.