A BIT of advice for Putonghua-haters Roger Lee and Arvin Robles (South China Morning Post, March 5) - go to a map and locate Hong Kong (Asia, East). You will find it is surrounded by a big country called China. In China, everybody makes those ''irritating quacking'' noises. What's more, Hong Kong will be taken over by the Land of the Quackers in a few years time and - oh, horror - the two English Language channels, catering to about four per cent of Hong Kong's population - may be further invaded. But I am being ironic. Really, I agree with Messrs Lee and Robles. After all, this is a British colony. Perhaps we should consider phasing out the two non-English channels (where they don't so much quack as yap). I. M. CHANNING Causeway Bay