The TV and outdoor activity, through Delaney Lund Knox Warren & Partners, coincides with a revamp of Capital's weekend schedule by its new managing director, Keith Pringle.
DLKW has created a TV campaign targeting Londoners aged 15 to 44. It features a range of real people responding to sounds in real environments across London.
The campaign is designed to build awareness of the promotion, which returns to the airwaves having last run in February.
Breaking on 27 September, across Carlton and LWT, the TV campaign is backed by London Underground poster activity featuring three executions that will tell listeners about the promotion, which asks listeners to guess everyday sounds and win money.
Carl Lyons, the marketing director for Capital FM Network, said: "This campaign focuses on listener reactions and the 'I do that' factor, a feature that is consistent in every successful radio promotion. The campaign has the listener at the very heart of it and ingrains Capital in the listeners' day-to-day lives. This is consistent with the decision to shift the style and media used in marketing campaigns to a fresh, non-corporate form of communications."
ZenithOptimedia handles media planning and buying.
Capital has also made changes to its weekend lineup, hiring the former BBC presenters Emma Forbes and Andi Peters to host the breakfast show.
Hit Music Sunday, the show hosted by the former Big Brother winner, Kate Lawler, and Peters has been dropped.
Despite recent increases in its London listening figures, Capital is facing an increasingly tough battle for London listeners against its rivals, including Kiss and Heart.
Capital also plans to change its evening and late shows to place more emphasis on celebrity news, dance music and guest interviews. A plan to play more music is also being put in place, with its Saturday night schedule featuring six hours of dance music uninterrupted by advertising.