PX4FLOW : The sonar has interference problem when arming

I ran into a problem about distance measure by PX4FLOW.
I set the quad on table, before arming, the distance (MAVLink #106) is around 83 cm, it is correct, when the quad arming with propeller and 50% throttle, the distance result become around 40 cm to 90 cm, very unstable.
I think I should figure it out before test indoor fly. Is it caused by ESC? or vibration?
Any help would be appreciated.