Green’s Dictionary of Slang

(Aus.) inside information, e.g. I’ll give you the deaf and dumb.

1999		G. Seal Lingo 91: deaf and dumb is the drum, as in give us the drum, meaning tell us the truth.
2002		Pete’s Aussie Sl. Home Page 🌐 deaf and dumb: the drum, inside information, eg. ‘I’ll give you the deaf and dumb’.