Have you put a sniffer before the frame relay box to see if this is memory moving to accommodate large blocks, or if this is legitimate traffic.
Sometimes when some idiot makes an MTU of 30K (I know the default is 1500) and then routs stuff to a frame relay box, you can see serious puking.
This can happen when there is a custom IP apps and a flexible configuration. (Saw this at a company in NJ... running ATMs for banks...)
Tim
Tim