MIDI express xt 2 channels continually flashing

[gandsnut]

I'm using an iMac running 10.9.5

There are 4 rack synths and two keyboards connected to the ME XT.

After power-on, MIDI channels 1 and 8 (Korg X3R synth, Roland D300 piano
respectively) cause the XT's "MIDI in" channel indicators to flash continually
at about 3 flashes per second. Power either off, and the flashing stops.

Playing the Roland sends appropriate MIDI channel messages to the rack
synths, which respond OK.

I've tried a MIDI message analyzer program, but it sees nothing in the way
of clock or SysEx.

I can't see anything in the X3R's global config to turn on or off to stop the
channel activity. More curious is the Roland piano seemingly sending
something via MIDI.

Any suggestions?

Thx