I Have a air dog 150 its always been very quiet, ive replaved the motor once on it and about a week ago its been whining really bad, and i was running a good 18psi out of it and it never dropped at all. Now that its whining its at 15psi and can drop to 12 or 13 easy under throttle, i got new filters comming on order to replace them to see if that changes and im gonna call AD tommorow to see if i can get another motor from them. i got my return line going into the filler neck and ive heard that sucking air can cause it to hum very loud

 

Mine wines a little but holds good pressure. I dont use AD filters on mine i run all fleetguard filters and they are 10 micron which flow better but dont filter as good as the 2 micron that some AD filters are.