NVH Noise Vibration Harshness issues are difficult to find. I doubt it is a front bearing due to the design ( tapered roller ) , when they fail there are more of a old roller skate gravely sound. Rear bearings ( double row angular contact ) make a more of less buzz that will change intensity when you load the car left to right.

What you are describing is something vibrating and going in and out of resonance. If you have a guitar string and subject it to vibration, it will resonate and make a sound when the frequency gets to the resonance point.

Cars make many frequencies at the same time. When the high point of frequencies consider, noise is amplified, when the are opposite , cancel each other out.

The usual suspects are motor / trans mounts that are crushing out, exhaust that has a failed hanger, something out of balance ( fan, drive shaft ) heat shield to tie bar.

My SL has a 36" ish long tie bar running from the front cross member to the body, in the center there is a 1" dia / 1" long rubber mount to hold the bar from vibrating. The mounts are broken and ,under certain conditions, it will resonate for a second or two. I'll get around to fixing it at some point but is isn't critical and I'll end up using industrial parts rather than MB.

Also, the microphone system you are suggesting does exist. It uses piezo electric vibration sensors placed near possible vibration sources. Some of these are wireless, some are hand held for use in diagnosing bearings in an industrial environment.