My synth is sending something about twice per second. ( guess) what can I use to figure out what its is ?

It could be a MIDI Active Sensing (Keep Alive) message. Some midi devices/apps send them to let other devices know the connection is still open. There is often a configuration setting that can disable them.

You can use a midi monitor (e.g. MIDI-OX) to see the midi traffic being sent back and forth.