Headers

Like a whistle coming

From underneath everything is tighten down

That's the sound of money being sucked out of your wallet for no reason-

Oh really, what you mean

I mean you are doing custom work on a fairly new car- why? and once you do some customizin' how are we s'posta know what's goin' on? now you have to spend more money to have a second opinion by an expert unless you get lucky and figure it out- that's what I mean-

Sounds like a leak from imperfect alignment of new header and gaskets? Recheck your work, adding a sealant if surfaces don't perfectly line up. Or return the header for a better made one! Don't know why you'd add a header to this underpowered Subie....

It is either a leak or the header or pipe is rubbing on something. A header on a Subaru, that's an interesting concept. ;)