Hi,
first point would be to check ALL connections are correct - by this I dont just mean a quick look. Unplug and replug and make sure all are fully home, thats every connection. IF these are connectors that can be opened then worth checking inside in case an earth/signal is off/damaged inside the connector.
I doubt its the blu ray player but can be caused by anything, so unplug fully to check that all cables and mains.
Is the sub powered? if so then power off, unplug audio input to sub and power up - hum still there its the "sub" or sub related. If no hum then its on the audio line.
With the sub off check the main speakers - still hum? If no then money n the Sub. If yes unplug audio input to amp,
still hum? then amp related (by related it could be mains borne)
With this kind of problem you start at the speaker and work back along he audio chain....speaker, speaker cable, amp, interconnect, pre amp, source cables, source.....
With a "no audio" fault you start at the source and work forward in the audio chain.
It is also well worth checking the mains plugs - make sure all connections are firm.
This may seem a big job but I have tried to cover all angles and your situation may only require some of the above......
I hope you find it of help.
Andy.