Helimax Voltage Users Please Help

[HW911]

I am having an issue which I think is the controller. After engaging the motors in attitude mode the motors will speed up and slow down to idle which is normal. After about 10 sec or so the front (seems to be) motors will speed up on their own to the point of lift off with out moving the throttle stick. It seems the quad is trying to correct itself while sitting idle in attitude mode.This happens sometimes in 3D mode but takes much longer. If I take off immediately it seems to fly fine but kinda risky if the motors spin up on their own and then lift off. I tried playing with gains on the bench and also checked and recheck radio settings. Setup is pretty straight forward.

I am new to quads only fly Heli's. Should I be able to let it sit idle with no reaction from motors?

This is the second one that does this. The first hobby services (Helimax) confirmed the issue and refunded money. Seems strange to have 2 different units with the same issue.

Any suggestions?

Thanks