First off, alot of people seem to think 2.4 Ghz radios are imune to interference, not true.
It could be the engine but I have to ask, was the receiver in that same crash?
I have had receivers that were in a crash that worked just fine until I fired the engine up. Hairline cracks will sometimes show themselfs under the vibration of a running engine.
PS: as hossfly suggested your switch could also cause this. Plug your battery directly into your receiver and see if it still does the same thing.