Ford Repair: 1991 5.0 HO chirp at wide open throttle, mustang notchback, tensioner pulley

Question
I have a 91 mustang notchback 5.0 with an engine that was rebuilt about 30k miles ago. Recently at wot, whether or not I am in neutral or in gear, I hear a loud chirp at redline. It is not the belt or the tensioner pulley they are both new (I just started replacing things as I suspected them of being the culprit.) Belt tension is tight. I assume it is something on the front of the motor. One of my friends said it might be the water pump, but mine is fairly new and I can't pinpoint where the sound is coming from due to the noise the engine creates at wot. The engine is mostly stock except it has msd coil, k&n drop in filter, and x-pipes with all emissions equipment still functional including smog pump. Any help would be greatly appreciated.

Answer
Sounds like the purge valve on the smog pump. It is located right on top of the pump,with a small vacuum hose attached. However, to be quite honest, it is really something that I would have to witness or hear myself. You said you have the MSD coil. You don't have the ignition box as well do you? The reason I ask is because they have little rev limiter chips that install in the side. I use them on my racecars, and I doubt you would have left it out.