Sreeching Sound, Front

I am getting a screech from the front of my 99 Disco TD5. Suspecting the alternator bearings to have resigned but I need advice. Do I start with the alternator straight away or there are other things that need to be checked first? Does anyone here know the specifications for the bearings should I need to have them changed? Any useful past threads on this?

when does it screetch, when stationary or moving? if a wheel bearing goes it squeals like a bitch but only when moving

Belt tensioner may be, but why do you want to know the specifications for the bearings.
Just Google bearing specifications that will keep you quiet for a few hours

have a look for rust coloured dust on the front of the pulleys. It may help narrow down which pulley is at fault without the need to remove the belt.

The screech is there there even when stationary but the pitch goes higher when the gas pedal is pressed, showing the suspect guy is related to the pulleys coupled to the engine by the belt. I will try to look for the rusty dust as has been suggested by one of the replies here. Worth the try.