If you start having trouble with your PP's I would suggest looking at the fluid. I had one that started making noise until finally it got to where it would not work at all. Yesterday I took the pump out and removed the plastic reservoir and when I dumped out the fluid I discovered a huge glob of stuff in it that looked like some kind of paste or something.
I live in Florida and we have a lot of humidity so I assume the glob was caused by condensation getting moisture in the tank. Evidently the environmentally safe fluid don't mix with water very well.
Lesson learned...change the fluid about once yearly to prevent problems.
Here is a picture of the Glob that came out of my PP tank. It was actually larger than shown as some had already went down into the oil drain pan.