Power steering pump rattle

There's some concerning noise coming from my power steering pump. It kinda sounds like it's running dry.
Before dumping money into a new pump I would like to hear your opinions. Can i just be something as simple as a clogged hose or air in the system?
Here's the video link:
It's a 98 Defender td5


Any advice is appreciated.
Thanks!

Is it 100% the pump and not the idler pulley ?
Water pump is run off the back if I remember correctly.
Are the pumps particularly expensive?

I'm pretty sure. Turning the wheel makes the noise worse.

You could pop the belt off and spin the idler by hand just to check. Cheaper than a pump.
Regardless it certainly doesn't sound very good that's for sure.

Cheap one seems to be £100 or so.

Yeah, I tried that. Idlers sound good.