I do a back wash once a week and the gauge is always at 12 -15...all the time. Is that a good thing? This week I even did the turn it on and off several times for about 30 seconds each time then I rinsed and it still sits at 12 -15. I have not seen it get any higher or lower. I also sometimes hear something in the filter like a rattle, not to noisy but it is definately there...what could that be? air?