Thread: Screeching noise from motor after header install

So we just installed headers onto the Daytona, and got it welded up from downpipe on, everything sounded good. Car started misfiring, so my brother replaced the plugs and wires. Now he's telling me when he WOT past 3500-4000 rpms, he hears a loud screeching noise coming from the motor.. and he has no idea what it is. But when he puts it in 1st gear and gently inches up to 3500-4000 rpms, it doesn't make the noise.. I'm confused. Any suggestions at what we should look at?

Maybe belt slip? Do any of the pulleys sound dry?

Probably a exhaust leak