Cylinder 8 chirps when fired.

[regislovato]

After replacing my head gaskets this last weekend, I got my '73 Mustang up and running, and noticed a chirping noise from my engine. I originally thought that the chirping could be from my belt, so I replaced it, but it didn't help. After listening closely, the sound seemed to originate from the mid to rear of the engine on the driver's side. I figure it may be a bad seal to my headers, but it only chirps under load (Although it could still be a leak from the header gasket). while trying to figure out what the problem could be, I decided to disconnect the wire to cylinder 8 for a moment, and the chirping stopped. Now, it had never chirped before I replaced the head gaskets, in fact I replaced the head gasket just to try out some copper ones I had my eyes on for a while.

Now then, I was wondering, would a leaky exhaust header gasket cause a chirp? What about a bad valve? I figure the valves are fine since it never chirped when I ran it before, but the fact that it chirps when it gets a spark under load... ...Let's just say I hope it's not valve related. By the way, I'm running a pretty stock 302.
thanks.