Low Boom-boom Noise From Under Car

After the big snowfall in Vancouver, I had my belly pan damaged, and I thought the soft boom, boom-boom, boom noise that started then was directly related. I had the belly pan fixed, but was disappointed when the noise was still there. It is a low-frequency barely hearable (I can hear it quite clearly, but my wife only pretends to hear it) soft boom-boom, like the wind is bouncing something under the car. Is a soft booming sound the noise a wheel bearing makes? It is not the engine, as it immediately stops when the car comes to a stop. Anybody experienced a similar sound? I never had a wheel bearing go, so I am unfamiliar with that sound. It started up fairly suddenly after the big snow. It doesn't seem to be particularly speed-related. This car is driving me slowly insane.

Ok, so what was the nature of the damage, and what was done to fix it? From your description, it sounds like a flexing in the belly pan, but as you well know, it is difficult to diagnose strange sounds in this setting. Maybe one of the side skirts that holds the belly pan was also damaged.

Wheel bearings do not make low booming noises. They have been described as screaming or squealing; not booming. This about the sound and what could make it. Low freq noise would lead me to think wind pushing on something.

Front or back of car?
at any speed or only certain speeds?
going straight or turning?
in gear only or in neutral too?
change in belly plate allowing air to run through where it didn't before?

Powderhound, one of the side skirts was damaged, so a new one installed and the pan was reattached. The sound after repair was exactly the same. Mike, seems to come from front, and the sound is pretty much the same whether I go fast, slow, turn, etc. Probably will get the mechanic to check it out at next oil change, soon.

Well, I managed to squeeze under enough to see...they left off a front screw, and the pan was hanging down about 3 inches, enough to catch air. That is the second mechanic in a row to work on the belly pan and couldn't manage to replace all the screws. I am on holiday, and haven't tested the car out, but I am thinking that was the culprit.

Thanks for the followup...It is always helpful for others to see the resolution to a symtom... Happy new year!