another mmm v3? also, does this happen in other instances? like what if you take the tx and rx to a place you normally arent at, have the rx just powered on from a rx pack, then test range... Also, make sure your rx isnt loosing power. I thought I had the same issue in my rustler, but it was my BEC shorting and cutting power to the RX
Same thing happens with my DX2.0 about 100ft down by my neighbors house. Its unexplainable and was a freak thing. My thought is a trucker with a CB radio was driving by and caused some freak reaction.
And as said before, a number of things can cause Spekky radios to go bazerk. CB radios are, as far as I know, the number one cause. Maybe like what happened to me, a trucker drove by and caused your DX3S to go nuts? Or maybe a plane/heli? Could be anything.