Align 450 Toilet Bowl Effect in loiter (DF log attached)

I am running a 450 size FBL heli with APM2.6, copter v3.2.1 which is the last version that supports APM.

During loiter, it experiences toilet bowl effect. I attach the log with photo of setup. APM 2.6 is mounted on 4 blue damper balls. See photo.
Since the GPS module is mounted under the rotating main bladeI, do the blades affect the satellite signal, causing toilet bowl effect ? See photo.

Align450FBL__APM2.6.param (5.4 KB)

The x and y axis vibration shown in DF log seem a bit high (outside -3 to +3 range).
z axis is more or less at boder line (-5 to -15). May these values be part of the cause of TBE ?

Heli has a small degree of tail hunting occasionally. I always turn the knob to 1550 pwm in my Tx.
Not sure if the motor speed at this setting is too low to cause tail hunting, which also creates TBE.

Any help is appreciated.