Pitch modulation by object thickness

Hi All, I am currently working on a project which I wanted to make as a proof of concept first. I need some help and am looking for experienced scripters to point me in the right direction.

The premise is this: There is a wooden board with an object behind it, the only way you can locate it is sensing its location using your ears. So when you knock against the board it will make a noise depending on its depth. If you knock against the wooden board in a location where the object is hiding it will make a lower pitched noise because it has more material to travel through before creating the sound.

Right now I have a fairly basic setup which means if a character walks up to an object and clicks it, it will play a sound cue. I think the next step is to find the location the actor was clicked on, create a ray trace opposite to the face normal which will then measure the thickness of the actor before it passes through its back face (and also any objects behind the first actor). Any suggestions or resources for the kinds of functions I would need to use to make something like that possible would be a great help. I will keep you updated with my progress.