Should be an easy one but I had more trouble trying to Google it than I expected. It’s the song you always hear in TV (especially cartoons) when it’s a fresh spring or someone is waking up etc.
I assume it’s something classical I just have no idea what.
Here’s me trying to whistle it. (Link goes to a site that lets you download a short .wav file. You might be able to guess what I’m talking about without even downloading it though)
Well, for whatever reason, I can’t listen to your .wav file.
But, I’m gonna take a wild-ass guess and say it’s William Tell Overture: Call to the Cows
I couldn’t remember the name but I searched for cartoon music, sunrise - found in less than a minute.
I hope it’s the right one.
Yeah that’s it, thanks.
Going back to the same site where I found that last one, it mentions that Greig’s Morning is also used for the same purpose.
Here’s the page
http://www.kickassclassical.com/classical-music-popular-famous-best-composers-a-z.html#Grieg
Oh…you’re welcome!
Actually that’s even closer to what I was thinking. They both seem very similar. The text on that page even says it is used “almost interchangeably” with the William Tell Overture.
That was my opinion too. I spent most of my first 18 years listening to large amounts of classical music (it’s all my mom listens to) and I still can’t tell the two apart (or remember the names).
You’re definitely whistling Edvard Grieg’s Morning Mood. I agree that there are some similarities with part three of the William Tell Overture (and knew before opening this thread that the answer would be one of the two), but they’re not that indistinguishable.
Before I even opened this thread I was pretty sure the OP meant “Morning Mood” from Grieg’s incidental music for Peer Gynt.
Other recognizable pieces from the same score are “In the Hall of the Mountain King” and to a lesser extent “Anitra’s Dance”.
Recent thread for identifying ubiquitous pieces of classical music. The William Tell excerpt and Grieg’s piece are both mentioned.
The other commonly heard spring/morning song is Mendelssohn’s “Song Without Words” op. 62 no.2, aka “Spring Song” http://www.youtube.com/watch?v=iwZJrpNPAhU
A much older thread for ubiquitous classical music: Classical music for Popsters - In My Humble Opinion - Straight Dope Message Board
You should be able to find most of that stuff on YouTube.
Morning Mood plays over the title screen of Peggle as the sun comes up. That’s how I know it. 
I think I’ve heard Beethoven’s 6th (Pastoral) symphony used in similar circumstances. Probably one of the first two movements. Could be.