Henry,
Welcome to the forum. From what you've posted, you have some pretty good background with X10 and you've taken some logical steps to isolate your problem. Lights that come on (or go off) by themselves can be a lot of
fun to track down. This problem is normally associated with significant hair loss on the part of the troubleshooter.
You've already identified two changes to your home system (addition of CFL and a new A/C compressor). Unfortunately, I (we) could use a bit more information about your system configuration.
I use the most simple remote control scheme- HR751 module, HR12A hand controllers.
I'm not familiar with the HR751 (and didn't get any hits with Google). Is this a automation controller similar to the CM15a. Could you have meant a TM751 transceiver?
- install a load-side noise filter (Lutron) on the CFL lights so they don't produce noise back into the house wiring.
Your addition of a load side filter to the CFL circuit is a good one. However I'm again not familiar with the Lutron models. Is it possible that these were intended for a different range of frequencies (i.e. they are allowing noise to pass though in the X10 range).
removed the control module from the wall overnight as a test to see if the problem quits. It did not.
Removed the control module overnight - which control module (HR751?)?
changing the channel for the offending lights. Curiously the channel I moved the lights to in this test (A5->A4) has another switch module on the same channel which does not turn on by itself.
Can you determine if these devices are on different 120V phases? You may have a situation where one phase has a significant amount of noise (CFL circuit) with the other being clean.
Do you have a phase coupler (active or passive) installed?
Sorry - a lot of questions without any answers. We'll try to work on that.