hi, everyone,

recently i bought hp 2309m and use its internal speaker for sound, fantastic result for the last few weeks, but this morning,
there is a noticeable humming/buzzing sound from the back of the monitor, can hear it when i put my ear near the back of the monitor.
but the humming sound gradually fade off after a while(maybe 45min to an hour later)

could it caused by the vibration generated by the internal speaker of the monitor?
i did so searching online, some said it could be transformers problem...
so should i send it in for checking? or it just a normal situation? hope can get a reply