Helicopter Pilot reported an NMAC during pre-takeoff hover checks on runway.

Narrative

We taxied out from the ramp to Runway XX at [Taxiway] 1 via [Taxiway] 2 and held short for landing fixed winged traffic. As the aircraft was landing; there was CTAF call for Aircraft Y taxiing from [Taxiway] 3 across Runway XY and we visually acquired it. As the landing traffic turned off the runway; we made a CTAF call for taking the runway and proceeded to taxi onto Runway XX and began hover checks. As we were finishing the hover checks another CTAF call was heard broken but understood 'MEDEVAC....' My Copilot suggested a clearing turn to identify the traffic and I saw distant bright lights in my side rear view mirror. As we made a clearing turn to investigate; we saw the fixed winged traffic that was taxiing earlier taking off towards us. We immediately landed from our 10ft hover and the plane passed over head us by approximately 150/200ft. No other CTAF call was heard. This took place at approximately XX32 local. It was unknown by the first CTAF call heard by the taxiing Aircraft Y that it was MEDEVAC otherwise we would have continued to hold and yielded the runway to them. Weather factors should not have precluded the other aircraft from seeing us on the runway and we never heard anything after their broken takeoff call.