High pitched squeeling when turning our wheel

Hi,
We have a 2001 Hyundai Accent 4dr that has just had it's last check-up, but, lately, every time we turn the wheel, we hear a high-pitched squealing noise.
We went out just now to take a look at it, and, it appears that either the belt is slipping, or, the pump is kaput. When we turn the wheel, at first everything is fine, but, then the top gear, connected to the pump, stops turning and therefore causes the friction on the belt.
I've tested the belt's tightness, and it does have some give to it, but, I was wondering how you can tell if it's not just the belt being loose, a helluva lot lower cost, or do we have to buy a new pump?

Thanks for the help! :Mrgreen: