Hum from Cable

[Dean Masters]

I am wanting to run a patch cord from the headphone jack on my TV to my PC 
to record some shows but there is a hum. I have Comcast cable. The patch 
cord is actuallly two cords with male plugs on both ends and a connector 
with two female plugs.

When I put headpohones in the jack there is no hum.
Is there something I can do to get rid of the hum?

Thanks,
Dean