I guess it's always possible that there is a component in the rotor head assembly that is generating some noise after the you disassembled it and replaced a part or two.

Keep this in mind tho, electric heli's are notorious for generating RFI signals. If you haven't noticed there are capacitors soldered across the poles of both motors on this ship. The idea is that the capacitors filter out the A/C RF noise before it reaches the motors, and in a servo, keep the controls from glitching all over the place. This problem is also common on gasoline powered heli's, and other than using a a PCM receiver (FM- like the AXE- is more susceptible to the RFI), the larger choppers will also solder a capacitor acroos the Hot and Ground leads of each servo as close to the servo as possible (or even inside it, like I did on my gas x-cell).

http://www.helibuf.com/reviews/xcell-gas.htm

Anyway, I'm having the same problem that you guys are, after replacing a blade grip and set of main blades. The chopper will lift off and then violently want to drop out of the hover, and you can hear the change in either pitch or headspeed (i'm suspecting pitch) when this is going on.

One problem that I found a few days ago was a bad solder on the hot wire leading from the speed control board to the motor at the disconnect plug.. it was concealed by the heat-shrink tubing.. the thing pulled apart with no effort when I was trying to trouble shoot a complete shut down of the main motor without any warning. Easy fix.

I'm going to give this thing a few more hours of troubleshooting, but if that doesn't fix it it's going right back to Great Planes to see if they are able to figure this one out.