[sprint_veloce]

If the pump has lasted that long it's a good one - I'd leave it. They're a pain to get out so you don't really want to change it if you don't need to. Typical failure is the bearing and that causes the seal to leak coolant. Often they get noisey once the bearing is letting go. I've never heard of the impellor clogging up, nor does the impellor fall off the shaft like many other pumps. So it's really just the bearing noise and leaking you should look out for.

Best thing to ensure long water pump life - adjust the belt as loose as possible while not slipping when cold.

 

[sprint_veloce]

Take the belt off and start the car and see if noise is still there - if it is it can't be the water pump. "Scratching" noise does sound more like cambelt tensioner bearing to me. Don't run the car for long with no water pump!

 

[sprint_veloce]

Yes will start and run fine, just no coolant movement and no battery charging. You only need to run it for 10 seconds to confirm.