Actually, I'm pretty convinced it's due to audio clipping
There is an option in XBMC labeled "boost volume on downmix". My dolby digital files are not bitstreamed to my receiver because of a XBMC bug. Because of that, looks like XBMC is boosting the volume. Assuming anyway because after I disable it I no longer hear all that clipping
I'm not sure how to handle this in WMC, though? If there is volume enhancements of some sort throwing things off.