Possibly, a misfortunate cat sleeping under the hood. This bang is probably a loose engine mounting bolt. The noise is probley from bad rod bearings once the oil pressure is up they quiet down.After it sits a long time(over night) the oil drains down and will be noisy It may last a long time just make sure the oil level is good
The engine parts are rubbing until the engine oil pressure builds up and the oil starts to lube the parts. Old oil, wrong viscosity, or a clogged filter can cause this to be worse than necessary.
Engine running hotter then 220 degrees can cause valvetrain noise. Bad fuel can also cause valve noise / PINGING sound. Ignition timing to high / Advanced to far, can also cause engine noise.
A bad harmonic balancer can cause a knocking noise. The harmonic balancer doesn't actually produce the noise, but it can cause the noise in the engine.
A bad compressor belt can cause a whistling noise while running the air conditioner. A bad engine can also cause this noise.
Perhaps a bug on windshield.
turn the engine off
Have someone check your Engine mount
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.
When you can not figure out why your car makes a strange noise, you take it to a mechanic.