So I just got a new P3a and I used a battery from my old phantom, its an Aftermarket PowerExtra battery. Immediately after powering on the loudest fan noise started, I was like wtf. Powered down and turned on again, same result. Powered up my old phantom that has this problem and side by side they now make the same high pitched fan noise. I believe the culprit is the After Market battery made by Power Extra, somehow it has made the fan turn on very loud. Hopefully this may solve some other peoples questions why suddenly there phantom makes this strange sound.