02 Outback ticking when engine under load

[Ryouko]

So I drove my sisters outback today and right away I noticed a ticking sound coming from the engine. Here is what I know so far.

Car:
02 Outback, bone stock, 87 octane, automatic

Sound:

Idling, coasting, holding a steady RPM in Neutral, put it in third and coast - no sound

When I give it some gas it starts clicking, it seems like the more engine load the louder it is.

I can't think of what it would be. If it was something in the engine, it would be happening when it is coasting. Something in the drivetrain would make the sound when I force it into third.
Any ideas? BTW, this might be hard to troubleshoot since I won't be down here for long.


[SOLVED]
The problem got worse and it was clicking all the time. I climbed under while it was running and felt hot exhaust blowing on my face. Right under the driver, the screw that holds the heat shield onto the exhaust header was gone. So it was leaking out a lot of exhaust and the heat shield was rattling.