Ok its an ae86 running a bigport aw11 4age.
I have just replaced my whole cooling system:
water pump
belt
radiator
hoses
So that is one thing that is eliminated...
It will only do it when lightly revving the engine from idle ie at traffic lights to take off. It will emit a nastily loud squeal (enough to make your ears ring if your above the engine bay.)
It will go away after about a second, but it is annoying the shit out me, not to mention my landlord.
I suspect it may be my timing belt tensioner pulley, as I tightened it the other day and it made one noise go away (sort of a clicking sound like a dying rocker), and since this noise has arisen. I have one from a 100kW engine spare, are these interchangeable (I haven't had the time to check this so I thought I would check before I replace another part that is working fine.)