Stablize is OK, Loiter with forward speed will have a severe vibration

We use copter 3.5.5 for our hexa-rotors UAV.
The Vibration is in good level in stabilize mode. but changed worse in Loiter mode with forward flight.
Can anyone help?
the bin file is as follow:

Did you balanced props, checked bad bearings and loose components, cables onboard ?

Yes, we did, we also arranged the cable in C shape to avoid magnitude interference.
We didn’t use vibration isolation for autopilot. we tried damping materials, the vibration level was getting worse.

Are you the same guy on RCG with the hex that has the middle arms WAY longer than the other 4 arms?

Yes, the middle arms are longer than the other 4 arms.