I get this ERRR sound every time i start my car. It seems to go away after a few seocnds or after i rev the engine but the other day it wouldnt stop. since then it has gone away but i have no idea what it is. Does anyone know?

Can you explain more? Where is the sound coming from?
Perhaps a video or sound clip would help a lot.

coming from the engine bay

Most likely the secondary air pump if you own a 2000+. It is located under the air box.

when is the last time you replaced your belts?

is the secondary air pump easy/cheap to replace?

water pump and timing belt replaced last summer at 84xxx

and btw i have a 01 1.8t quattro

Well when it becomes a problem it should throw a code. It really only comes on during idle after a cold start. As the car gets older you will notice it come on more often and it should turn off once the car is warmed up or driven.

A- i was talking about the accessory belts, it just sounds like belt squealing to me. the timing belt doesnt make a noise, it has teeth.

B- you never said how many miles are on your car right now so 84xxx means nothing to me.

94k on it now

To see if its the sai pump or not, just pull the fuse or the connection.