Step one is to determine what is causing the noise.....it might be the typical low rpm "pump rattle" and it might be a sign of something going south. The fact that adding fresh grease makes the noise stop indicates one of two things....either the noise is i'n the bearing, or the bearing is worn out (but quiet) and when it's flopping around, the shaft is moving causing the impeller to contact the housing...adding grease takes up space and temporarily tightens up the bearing.
Regardless, I would tear it down and see what's going on.
It's really not to hard to replace all the parts. short version: pull the bowl, pull the impeller, remove rope seal, unbolt front bearing cap, smack shaft forward with a soft mallet and pull the shaft/bearing assembly out the front. Remove old bearing, press on new, installation is reverse of disassembly.
The hard part arrives when attempting to "blueprint" the pump.....ideal radial clearance between the impeller and wear ring is .025", and if using a shouldered wear ring you've got to shim the impeller back to set that clearance as well.....when the thrust bearing comes under load, it deflects and the shaft/impeller will walk forward a bit....need clearance so it does't hit. I generally buy an undersized wear ring and standard size impeller and re-machine the impeller while on the shaft to control the runout of the assembly....this is a procedure skipped by some shops that I feel is probably most important for pump performance and longevity.
If money is tight...don't worry about the impeller or wear ring for the time being....just do the gaskets, thrust bearing, and bowl bushings.....that will keep the rest of it alive until you're ready to do the rest of it.
Start with pulling the bowl and impeller, take it from there. Disconnect the driveline and the while applying forward pressure to the shaft, spin it and feel for any rough spots....if there at any, change the bearing.
