Hi Corporateangel,
If I have to guess, I think the van with the loudspeaker that comes around your neighborhood was yelling annoucing in cantonese or perhaps other local dialects "Buying Old Newspaper, Buying Old Newspaper", and and they drive around the neighborhood, they broadcast the message and you will see people who have collected old newspaper bringing them out to sell. It's a way for the people in the housing estates to recycle their newspapers. Cheers!