What engine are you talking about?
Assume a V8, if so, these pumps appear to last about 75k miles before the bearing seal starts to leak slightly into the bearing, then shortly there after the bearing starts getting very noisy.
I just had to replace the pump on my 2008 4.8l. Not a hard job, not an easy job. Pump is only like 5-6 bolts, but one bolt is behind the crank pulley and most people have to remove the lower crank pulley. I have smaller fingers/hands so I was able to do the job with removing the lower crank pulley, but I can get some pretty tight things done.
Also you might consider doing this proactively if you have a N62 V8 and have the water pump off the engine.
Bimmer Fix | Coolant Pipe Repair System
Hardest part of the coolant pipe was sanding down one area so the pipe would slip in the engine without much resistance.
I am glad I addressed this now, may not have ever had a problem, but this hopefully keeps me from having the coolant pipe leak in the future.
BTW, my pump started with a slight knock the day before I had to take a 2500 round trip. I took the trip and crossed my fingers. Pump got louder as the miles accumulated, however, I mad the 2500 mile trip before the pump failed totally. So I was able to change the pump before the seal or bearing fully failed.