Basically, I'm looking to make loud noise

I would try toneAC, two Arduino pins, and a poor man's H-bridge (two transistors).
That could give the loudest sound with the least parts.
Leo..

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You mean, four transistors!

No, two.

Imagine R2, Q1, R1 (post#20) twice, for two Arduino pins. With the speaker directly connected between the two collectors. And maybe a capacitor across the speaker to remove digital harshness.
A poor man's H-bridge is frequently used for bi-stable relays.

Collector resistors could be 220 or 330 ohm, and base resistors could be 10k.

Must use toneAC, which generates two PWM signals out of phase.
Leo..

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@Wawa Thanks for the great suggestion! Do you have a recommendation for transistors that are well spec'd for my use case for ~10W at 12v

Just use medium power NPN transistor, like the 2N2222, BC337, etc, for that simple H-bridge.
And don't expect 10watt output from that circuit.
You can't push 10watt of digital noise in a 10watt speaker anyway (more like 1watt).
You might already have enough noise with a 5volt supply.
Just try it. You can always upgrade to a class-D amplifier.
Leo..