MAG3 Pump Placement

[Shadowrider]

I put a Remora skimmer on my 72gal bow front and hung the MAG3 pump inside the tank which really looked ugly but worked. I figured that aside from looking unsightly the pump was also introducing some heat into the tank which I definitely do not need with outside temps nearing 100°F during the day. I used some PVC pipe and fittings and plumbed the pump to hang outside the tank. It's working OK and the skimmer is doing it's job, but, I've got some air going through the pump and it is also humming quite loudly. I have a T fitting with a screw in plug on the inlet line so I can prime the pump. Question is, should the pump be hanging below the level of the inlet tube? Is having it hanging above the level causing it to suck air and be noisy (possible cavitation at the impeller?). It wouldn't be a huge problem to move the pump lower but I don't want to do it if it's not necessary.