My Northstar pump periodically seems to have an increase in the decibel level of it's background noise level. I can only describe it as follows: its louder than normal, and seems "coarser", not as smooth, as if there is some air or other material slogging around in there to make it louder. Also, I have this curious observation - if I apply backpressure on the system (on the order of 2 psi), by slightly closing the valve to the pool return jets, the pump gets quieter, more like the normal level of background noise from the pump.
Any thoughts on this and whether it represents some sort of problem? Has anyone else experienced this?