hrm, one of the hardest things to fix, and I have to make a post here today, because it's like the only CP question in the forum today =P wow, what a big day for the cx helis =)

anyways, a couple of things, how is your antenna on the Rx side wound? It's not around the tail boom or anything is it? you haven't shortened it or modified it? Have you checked it for continuity? Sometimes the rx antenna can have a short in it even if the insulation has little to no damage. Someone had already mentioned reseating the crystals, how did that go? Have you tried your heli in a different location, onee that would likely have less RF noise?

If all that is the case, I would unhook everything, and then just add one part at a time and see if you can't isolate which part is causing the problem. Also opening up the Tx and looking for cracked or frayed solder joints, and checking that the antenna is screwed all the way in.

what about your Tx batteries? How are they doing? Measure them in the Tx with it on and see what kind of voltage you are getting.

Alot of these things have probably already been said, but I am just brainstorming, trying to come up with something that you could look at =)

If it ends up being something like the main or tail motor, there are quite a few good fixes for that.