Hi,

You may have loosened that aluminum hose going from the air filter to the exhaust manifold.
It goes under the radiator and bends into a 90 degree angle at the frame.
There is supposed to be a clamp hold it tight around there.

Stretching the hose can cause slack between it and the air filter housing so it creates a buzz.
Just rearrange it or zip tie it under there.

That the only thing that I think could buzz or even moan under the hood.
Now a thumping clanking noise is a real eyebrow raising noise.
That's when the alternator's bracket becomes too loose!
That's when it pays to have a voltmeter mounted in the dash too!

Phil