A lot of my favorites have already been taken. Loons are great. An elk bugling at 0200 less than 300 yards from your bedroom window, because he's pissed off at an approaching thunderstorm set me on edge. My window is less than 60 miles from downtown Cincinnati.
Some that have not been mentioned:
1) The unmistakeably sound of a 250 lb whitetail buck trundling through drive leaves on The Opener.
2) Bucks fighting. It sounds like two drunks throwing up while doing a Morris Dance with hatracks.
3) Turkey's gobbling at close range are electric, especially when they turn their heads directly towards you and give that final "I'm comin' honey!" gobble.
4) However, for shear 220 volt excitement, I once had 8 jakes come in on me and for the longest time, I could not figure out what it was. It sounded like a half-ton bull bellowing, or perhaps a piece of heavy equipment starting up. They were gobbling, but it was bad gobbling and out of sync. When it came my way, I was scared.
5) The topper of the toppers is getting a surprise spit and drum from a love-lorn gob in full strut just behind your left shoulder. Few people besides turkey hunters ever hear one, and my first reaction was that The National Guard had their helicopters up mighty early. My season started this way this year. I had a tag filled within the first 20 minutes of legal hunting.
Here is a sample:
You need good speakers to hear it. In reality It is infra-sound that you feel more than hear, much like CH-47's or UH-1's do long before you see them. If you hear one with your shotgun in hand, it means God has ordained you are going to get a chance to shoot and it's up to you whether you close the deal.
Honorable mentions:
Screech Owls on a limb just off your treestand an hour before first light.
Turkeys roosting on your stand, and deciding to hold there until you are up the ladder and climbing in.
The sound a buzzard makes on a low pass over your head while you're taking a nap-- just checking to see if you're still breathing.
The sound a gazillion migrating birds make when they pass over you in a black wave. It sounds like distant surf.
An unexpected waterfall that does not show on the map.
A whitetail doe sticking her head in the bedroom window and snorting at you at sun-up.
