Saludos mauyc,
Rule pumps are very good & reliable, but all pumps I have seen are about as good.
You can remove the plate which covers the impeler ( bottom ) and see if it has something stuck in the impeller area. If if still sounds odd, replace it. Peel some of the wire an make sure its not corroded. Its a good idea to replace the float switch if its old, get one with a protective housing.
I prefer to have more ( smaller ) pumps, on separate wiring, than one big one.
I run one 500, and a 1500 with the float a couple of inches higher, in the aft bilge. And one 360 on the mid bilge. ( Remember the current draw ).
I mount all my pumps with a screen around ( like a spagetti draining screen ). For the 1500 I used an inverted plastic tupperware boul with many many 1/8' drilled holes, and never have to clean the pumps.
Juan