DISTURBING reports have reached Keeping Posted of an incident in the newsroom of Metro Broadcast, located in the bowels of a shopping centre in Hunghom. For the benefit of readers it should be pointed out that Metro's subterranean headquarters bears a people-friendly design, with many of the studios having glass walls that open out on to the mall enabling curious shoppers to peek in at the talking heads and news hens at work. Beavering away at her computer terminal preparing an item of news for the forthcoming hourly bulletin, a news reporter was distracted by an urgent knocking coming from the other side of the glass wall. Turning towards the source of the noise her eyes met the rather unnerving sight of a pimply youth unzipping his trousers and dangling his, er . . . what's-it at her before fleeing into the distance. The story appears to have reached the gleeful ears of the guys and gals at Commercial Radio, Metro's arch-rivals. And yesterday its Chinese channel, CR2, did a wickedly witty on-air parody of the incident. Needless to say this certainly was one instance when the term ''news flash'' took on a new meaning.