After blowing up across the globe earlier this year, secretive US social audio app Clubhouse is said to be in funding talks based on a valuation of the business of US$4 billion. In January, it raised $100 million in funding that valued the company at $1 billion. Just a year old, Clubhouse is an invitation-only audio-based platform where users from all around the world can join literal chat rooms to participate in what’s effectively a live, free-flowing podcast. The exclusive app has attracted several high-profile names, including Elon Musk and Oprah. Facebook boss Mark Zuckerberg is also said to be interested, and the tech giant is rumoured to be developing its own copycat app.