Mysterious sysex events - logic pro 7 with micro express

[Sticky Fox]

I'm running logic pro 7 on an aluminum imac. There is always a periodic "blip" on the host output LED whenever the system is powered up. It is about one message per second, but they do not come with perfect regularity.

When I'm recording in LP7, these messages get picked up as "sysex" packets, and are recorded on any channel that's active, even if it's not record-enabled, and even if it's not a MIDI channel. Weird.

I searched for this problem, and lo and behold, the last person to complain about it was none other than yours truly. I can not for the life of me remember how (or whether) I solved the problem. However, it appears that before it only happened while clockworks was running; now the problem is there all the time.

Muting sysex messages does not eliminate the blinking or the recording of unwanted data. I've tried reinstalling the drivers and reinstalling logic, but there has been no change. I can make the problem worse by fiddling with the routing and timecode settings, but I cannot make it any better.

Does anyone know what these messages are, and how to eliminate them?