Edit UDKSystemSettings.ini:
My Documents\My Games\Chivalry Medieval Warfare\UDKGame\Config\UDKSystemSettings.ini
Look for [SystemSettings] (not one of the bucket subsections)
Look for:
SoundMinCompressed=0
change this to a higher number e.g.
SoundMinCompressed=3
(you can go up to 4 or 5)
Seems to increase FPS for many people on lower systems