bad coil springs
back struts are bad or exhaust is loose
Muffler loud noises
If the 1999 Suburban noise is a sort of loud banging noise, the problem could be that the engine have jumped time. Jumping time would cause the noise and jerking in the engine.
An air intake house can be the cause of wind noise underneath a 208 Mazda 6. The problem could also be a bad seal on either your window or door gasket.
I believe that an engine can create a noise underneath the middle of the hood....
The most probable cause is poor fuel or water in your fuel. This could also be due to the timing being out of proper adjustment.
wheel bearing or it could be the carrier bearing as was in my case
have you checked your car for aliens?
With out hearing it, It is hard to say whats wrong. But the most common noise like that would probley be a ROD knocking. Time for engine overhaul.