C'mon folks, you're missing the obvious one - 'Junk Of The Heart' by The Kooks. That's got the whistle, the indie vibe, and was pretty much on every playlist a few years ago. Bet my vinyl collection that's the one!

Have you considered 'Young Blood' by The Naked And Famous? While it doesn't have a whistle throughout, it's been mistaken for those that do because of its synth sounds. The indie scene of a few years back had quite a number of tracks with distinctive whistle sections – 'Janglin' by Edward Sharpe & The Magnetic Zeros, for example, or the more obscure 'Generator ^ First Floor' by Freelance Whales. Could also be worth checking out songs by Beirut - 'Postcards From Italy' has a whistle and indie vibe, not as mainstream but definitely catchy.

Definitely 'Whistle' by Flo Rida. Indie masterpiece. Kidding. or am I? ;P

hmmm indie whistle... maybe 'Let Her Go' by Passenger? not exactly the whole song but it's got a memorable whistle for sure

I'm throwing a wild guess out here with 'Pumped Up Kicks' by Foster the People. Not a whistle through the whole track, but it's definitely indie and was impossible to miss a few years back.

Your description reminds me of '5 Years Time' by Noah and the Whale. Fits the indie, upbeat whistle criteria but it might be too known. If not, you might want to check bands like The Lumineers or Of Monsters and Men, they've had whistle tunes before.

oh man, sounds familiar, what if it's 'Fitz and The Tantrums - The Walker'? that song's whistle is top-notch imo. hope that's the one you're lookin for!

Could it be 'Home' by Edward Sharpe & The Magnetic Zeros? That's got a super catchy whistle part and it was everywhere for a while. Fits the upbeat, indie vibe.