A loud wet fart!

Not your own, I assume?

oooohhhhhh yeah.

A really big rumbly V-8 or even a 12, that you feel in your guts as much as hear with your ears.

I can't help that silly VROOOM grin.

Bird sounds at dawn
A babbling creek on a sunny day
A thunderstorm while I'm bundled up in my recliner or bed
My cat purring while she kneads my leg or arm
My 6yr old's belly laugh of delight
My partner practicing a riff on his guitar
Ocean waves rythmically washing ashore while I sunbathe, drifting in and out of sleep (and other beachgoers laugh and chatter in the back ground)
Rain pattering on the roof (and I don't have to go anywhere!)
Music playing while driving my corvette with the tops off