Howling Noise From Air Filter Box

Back when I had a drop in filter, the seal wore off of mine. It never caused any noise. I don't see how it could make a noise to the magnitude you are describing.

It very well could be the IAC.

Look at the hose between the IAC and the intake tube. Does it still have the box piece, or is it just a piece of hose?

The howling comes from the resonant frequencies that the incoming air can cause in the IAC and IAC inlet hose. Something like when you blow over an empty bottle. That's why it has a box in the inlet hose from the factory, to break up those resonant frequencies. My car used to do it, but it was from that inlet hose; with the way my supercharger is, I couldn't run that box and had to just go with a piece of 3/4" hose. It used to would howl like crazy, just like what you're describing. Touching the gas would often make it go away. To solve it, I put a smaller piece of hose inside my 3/4" hose. Still flows enough air for idling, but that different inner diameter breaks up those frequencies. It still does it on occasion, but it is much quieter and I think I'm the only one that would even notice it.

That being said, I've read many times that the IAC itself can cause this to happen. So if you still have that stock box on the intake, I'd guess the IAC is what the problem is.