jcpearce wrote:

This is without the system connected to any of the sensors, just
turning it on and with an external battery so it is physically
isolatedseparateithin 6' or so it causes interference. Rotating the
motherboard
does not help either. Thanks for the reply.

Possibly try remotely mounting it back in the fusilage and running
fiberoptic to it. You can get inexpensive hobby FO and FO to rs232 modules
designed for experimenting.
Other than that try a non-aluminum case and use feed thru caps on all leads
and ferrite beads also. try some additional filtering on the PS and/or try
using separate PS for processor.
Just some thoughts.
John

ps those hobby aluminum cases do lousy for rfi prevention!