Hi,
It could cable as Nodsu suggests as they are not making these items to last or withstand any punishment. The headphone & other AV sockets the manufacturers use (not just Sony) are crap. I know this from my days as an repair technician in the audio/video trade. Usually the solder gives or at worst the pads come loose. Generally, resoldering the socket provides a cure. If the socket needs replacing it is not an expensive task to preform but time costly. Any job today which is labour intensive will be expensive. If you have to go down this road and the socket needs to be replaced then in future I would suggest that you also purchase an extension cable or have one made up of ~3-4 inches with an headphone plug and socket and use this to plu your headphones into rather than the laptops headphone socket. That way you can easily and cheaply replace the cable accessory.
Regards
PFJ