Do you have access to a TDR? (Time domain reflectometer).
It's used to scope coax cables, and check the continuity of the signal wire, as well as the dielectric. If there's any breakdown it will show up.
Does the radio pick it up if you disconnect the aerial input to the T/R?
How about if you disconnect from the aerial, but leave the T/R connected?
Maybe there's something switching on at 2200 on that engine type - a governer perhaps? What's max RPM on it?
Be interesting to get a spectrum analyser on the output of the T/R whilst it's doing this, and see what the frequency band was...