what does an exhaust leak sound like

sounds like an exhaust leak to me, check all the connections on your exhaust.

A leak by the headers can sound like the fingernail tapping. Is it only when cold? When mine leaked at the headers, it tapped all the time.

I'm not sure about the other symtoms you described.

Tick Tick Tick. You'll be able to smell it too.

A tapping or ticking sound. Depends on how bad the leak is. If its bad enough, it's unmistakable. I noticed a tick after I went to the track last. I looked closely under the hood and I noticed exhaust under the hood on the passender side. Turns out that two of my header bolts loosened up big time on both sides near 3 and 6. When I say loosened I mean I pulled one right out of the header with my hand. One more launch and it would have been gone. I checked them all and few others were a little loose as well.

My passenger side gasket did not make it. I cranked the bolts back down, hoping that the gasket survived, but I still hear a faint tap. I am going to try and live with it for now. If it gets worse I will change the gaskets, but I am trying to hold out until I get my new Trick Flow heads and intake. It's my own fault, because I know better. I did not go back and check the bolts again after the 2nd time. I should have rechecked a couple week or so after the install and periodically after that.

You may only have the exhaust leak when the engine is cold. If the leak is currently minor, as the exhaust heats up, which happens fast, the ehaust may be expanding sufficiently to seal the leak. Check your header bolts and x- or h-pipe connection to the header collector.

I had to re-tighten my header bolts on Sun night. I heard an exhaust leak over the weekend. One of my bolts was also so loose that when I made a very slight turn to the left, it came out.