Sudden appearance of NOISE in internal compass of autopilot ( SOLVED )

I had pixfalcon set on 600 size heli which flew great. Then I needed to change bearings of the main rotor and the tail rotor. Since the autopilot was installed at the rear of the the heli I had to take it off which was reinstalled later. However now I see that the internal compass of the autopilot has a huge amount of noise. The external compass is fine. Since I am using better quality bearing ( from synergy, earlier I was using cheap hobby king stuff) so vibration should not be the issue. In fact I can see the IMU.ACC has the same amount of vibration as before. Also the current consumed is same as before. The compass noise is so bad that I had disable the internal compass ( set COMPASS_USE2 = 0 ). Then it works great. My only concern is why this is happening. Has someone else encountered this. Has the magnetic sensor chip been damaged? To show you an example here is the log of earlier run when there was not noise and log now with noise. You can see the huge difference.

Now when the internal compass is noisy.

Actually this is not really an issue. I disabled the motor and armed the heli pretending to fly it. Then the log generated shows no noise at all. This point to the fact that it is either due to vibration or motor interference to the compass. I will investigate it further. Hardware is definitely OK.