Mini Z AWD out of control - HELP!

Hi all,

I have 2 AWD Mini Z cars. I haven't run them for a long time, because I have a full-time job and haven't got much time to play with them.

Last evening I finally found some time to run them in my living room.
But while running one of them, I experienced that sometimes it completely goes out of control. Things like: running the motor when I haven't even pull the trigger on my remote control. Also alot of noice came from the servo. This car also has the stacked FETs upgrade (4x2)

Initially I was worried that the receiver on the car was damaged. So I tested my other car (with stock FETs) to see how that one performed. My second car ran a little bit better, but went out of control too from time to time (like running motor a bit without pulling trigger).

What could be the problem?

Is this a problem of the receiver on both my cars or is my remote control just broken?

Please help me.

Yours faithfully,

Ricky