Sounds like it might be a pump, it's not the engine belt, might be the AC pump, but the sound is there even when the AC is off, I'm no mechanic, I'm pretty hamhanded really, when it comes to this.

The sound is audible when the car is just idling and it increases in intensity when the car starts moving but when I go faster than maybe 50kph it stops, possibly thats simply due to engine/road noise.

Here's a picture of the engine, I've circled the areas where the sound seems to be coming from, anyone know if this might be something expensive to fix, or even dangerous to leave unfixed?

 

get a chunk of heater hose and stick it in your ear. Each accessory until you determine. It is possible that a bearing went out on the alt. or somethine of that manner.

 

Thanks, I'll try that, it's been quite hard to determine where the noise was coming from.

 

does the noise go away if you run the engine (briefly) with the belt removed? also with the belt removed, spin your accessories by hand and see if you can hear anything out of the ordinary and check for any play in the pulley/shaft. dont forget the idler.

 

I use a broom handle. I put one end on the each accessory then stick the other end up near my ear. This usually narrows it down enough.

Just be careful not to stick anything into the moving parts!

It could be any drivebelt accessory - possibly bad bearings. I'd check the alternator, AC compressor, Air Pump (below the AC compressor), Tensioner, and pump.

 

I had the same problem on my 89 RS V8 with serpentine belt. It turned out to be the water pump seal/bearing. All I did was spray some WD-40 behind the water pump pulley close to the shaft and it went away and never came back.

 

I did it with style and bought one of those stetoscopes you can put to engine parts to localize things like this, definitly seems to be the alternator.

 

I find those GM style alternators don't last.

Get a replacement with a lifetime warranty. If you keep the car for a while, you'll be glad that you did.