Yea, probably some resonance in the IAC tubing. Try holding and squeezing/pinching the larger of the three hoses that hook up to the accordian hose. (The smaller 2 are PCV) You should feel the vibration most on this hose and pinching the hose is similar to installing the TH fix. If the sound is coming from somewhere else, use a large screwdriver as sort of mechanics stethescope, "listening" to the handle, and probing for sounds with the tip.
