There's a plethora of music that fits the description. However, considering the distinctiveness of the didgeridoo and the term 'down under' that you mention, it would be beneficial to know if any other instruments are featured, the genre of accompanying beats, or any other lyrics. Such specifics could significantly narrow the search. Moreover, various indigenous artists have utilized the didgeridoo in fusion genres; an example that springs to mind is the work of David Hudson. Insufficient information leads to conjecture rather than a conclusive identification.

I reckon you heard 'Under the Sun' by The Didjeridudes. They're not that well-known, but they've got this one track with didge that'll knock your socks off. It's got the word 'under' in it - could be what you're thinking of!

lmao probably just some random guy blowing into a vacuum cleaner hose. 'down under' could mean anything, you probably imagined it while munching on those BBQ snags.

yo i think my cousin plays that kinda stuff...chill but sick beats. can't remember the name but i'll hit you up if he knows, ok?

Hey, could it be 'The Didge Song' by Outback? Their style is a fusion of indigenous music with contemporary beats. The track doesn't exactly say 'down under' but it's in that sphere. Also, could be something from Ganga Giri, they do a wicked mix of didgeridoo with electronic music. Tunes like 'Bayami' or their remix tracks might be what you're looking for!

sounds like you might've heard something by Xavier Rudd? He's got a few tracks that blend didge sounds with some cool beats. Check out 'Spirit Bird' maybe? or 'Let Me Be', not exactly 'down under' but has a similar vibe!