The question why the a/c did not return to london earlier has already been answered multiple times in this thread, but I'll try to repeat some points, in no particular order
1) Because a/c are meticulously maintained and inspected and the expertise of professional engineers carries more weight than "noises" heard by random people
2) Because door seals quite frequently have minor leaks which create noises, but in no way endanger passengers or the safe operation of the aircraft
3) Because pilots have better means available to verify door closure and monitor pressurisation than "noises"
4) Because it takes a lot more than noise to depressurise an aircraft
The a/c landed safely, no one was injured, and by now all pax have arrived safely in singapore. Whatever happened to the door will be scrutinized very, very carefully.
One of the more surprising things about this story is how critical Singapore Press suddenly seems to be towards the flag carrier. I can't say a free press is a bad thing, but lets hope they'll report not only freely, but also based on facts.