Some wierd noises…

Hi all, we're getting some odd noises off the van;

Stuff that’s happened recently that maybe could have a bearing on this:

—Belts replaced while injector was being removed for servicing. Do they need tightening soon after replacement?
We've had the belts tightened but this didn’t work. Should I just tighten them more? Can you over-tighten them?

—We had a coolant leak and overheat. Doesn’t seem to have affected the performance so I don’t think we cracked the head.
Could an airlock in the cooling system produce a ringing?
Could steam heat from leak affect the non toothed belts?

Can anyone think of other stuff that makes uncharacteristic noises?

If anyone has ideas we'd like to hear more. Mechanic's faces cloud over with this kind of thing as its usually impossible to find so I'd like to go in with more than ‘my van’s making a noise that only I can hear’

Sorry if this is all a bit waffly and impossible to figure out over a forum but I thought I'd give it a go.

Cheers
Marko

Edit: The noises are coming from the engine compartment btw : )

Screeching like a worn clutch bearing? Could be the exhaust manifold blowing, noise will be in tune with engines revs.
Squealing could be the idler pulley bearings or indeed the wrong belts/tension, noise may come and go.

need to know is this a mettalic noise?

Not sreeching, two noises really. One sounds like a belt scraping and is intermittent.
The other is a ringing like old tvs would when the channel had shutdown for the night. A soft sine wave tone.
Its there most of the time stops briefly when changing gear… which now you've mentioned it could be transmission related.

Update. Turned out to be the power steering pump. Had a 2nd hand one fitted and a perfectly silent(ish) trip back to London! Hurrah!