External pump capable of being mounted on wall?

That is not a good idea. Check valves in saltwater applications are not recommended, it does not have to be a catastrophic failure, even a grain of sand will drain the line and burn the pump up. Both check valves and centrifugal pumps are not designed nor intended for this use. Plus the check valve is now a restriction on the suction side of the pump which is a no no and will lead to other problems like cavitation and noise production.
If you are going external, drill the sump and try to place the pump suction so it is in a straight line with the bulkhead for fewer fittings and restrictions or oversize the suction side to account for friction and suction losses. Also keep the water in the sump return section high enough you do not experience vortexing or coning and cavitation and resulting pump wear.

Suction lifts are not something well dealt with by centrifugal pumps unless they are specifically self priming which is a completely different design and almost always very energy inefficient so high wattage per gallon pumped.

 

Reefer Bob,

The Sorbothane is probably best ordered from sorbothane.com as I haven't found anywhere that sells it. It's not real cheap, but it works better than anything I've used thus far.

The comments regarding having the pump at the proper level are indeed valid. I'm not real impressed with the Pan World 200PS I'm running...it works fine, but it's on the noisy side (fortunately it's housed outside in an equipment shed).

The quietest pumps I've used are ReeFlo Dart, Iwaki MD40RXLT, Little Giant 3-MDQX-SC (I found the next size up to be loudish), and Sicce Syncra Silent series pumps.

 

Ok I get it as how the pump doesn't pull the water up to it or lift it. But it's cause water pressure in the sump keeps it wet & ready to run. Yea I didn't know check valves were that unreliable. Well u seem to of shot down every idea I had. I'm glad u did. Thanks again. Haha