Loud tone when throttle increased

I know how to start the Osprey from a cold & dark condition; no problem. Have done it enough times and I can get airborne fairly quick. However, as soon as I throttle up enough for the aircraft to lift off the ground, a very LOUD, continuous tone begin blaring that does not quit until the aircraft main mounts touch the ground again, and I reduce throttle settings. I am not seeing any warning lights lit up, nor any cautions whatsoever. I figure it is something easy to spot, which is probably why I am missing this.