Holey exhaust manifold Batman

I was under the ole Dodge this morning changing the oil,and as I looked up to screw the oil filter back on,I noticed what looked to be a hole in the bottom side of the exhaust manifold.It is in the flat section of the manifold around where the #1 and #2 exhaust runners meet, just before they merge into the collector and start turning downward. I have always had what I thought was a small exhaust leak, because of a slight ticking noise.Now this hole is about half the size of a dime.I stuck a small screwdriver up into it a good 2inches.I put my finger over the hole while the engine was idling(before it got too hot)but didn't really feel much air pressure. Nor do I hear alot of exhaust leak noise. With a hole that size you would think it would be making all kinds of racket. I guess my question is, does a stock manifold have some kind of double wall built into it,or is the hole between the two runners that is covered by the casting? I have never had just the exhaust manifold in my hands to see how it is designed.Somebody help me!!