Hum Having humming sound from the subwoofer. What could be the source? Could interent cable nearby be causing the problem?

The loud humming is the sound of AC mains - clearly your amplifier is receiving an input from somewhere and possibly into the front end.

The hum could be induced by radiated energy from nearby unshielded equipment, it could be the result of an accidental hum-loop or could be because the amplifier power supply has a fault.

It is usual practice with amplifier construction to ensure unused inputs are shorted to ground by switching or by additional contacts and wiring at the input sockets. High gain high impedance inputs can cause a great deal of unwanted noise if they are not shorted.

I suggest you read the instruction manual and perhaps Google a few hints and tips about amplifiers and stuff.

I suspect the amplifier is damaged. This is not an easy repair to do unless you are well versed in audio electronics. I would recommend a repair shop to look at the subwoofer amplifier.

The symptom sounds like an open signal shield somewhere and the cable is acting like an antenna for airborne electrical noise.

Disconnect the RCA cable at the sub. Is it still humming? NO? Problem is external to it. YES? Internal. Broken ground somewhere.

Recheck all connections making sure to twist the RCA head as you install it so oxides will be worn off.

Consider what may have changed in the environment regarding electrical devices, motors, magnetic sources. Ensure signal and speaker wires as ar not running are as non-parallel to any power cords as practicable.

Disconnect the input and see if it hums in the absence of an audio source. A bad audio cable shield or unwisely-routed audio cables will allow entrance of unwanted signals from external power sources, magnetic fields, even dimmer-controlled track lights. Sometimes, simply reversing the orientation of the ac power plug can eliminate humming.

Subs don't go to a variety of connections on the amp. Let's stop guessing and stick with the prescribed one.

Register and download the manuals for free at retrevo.com

http://www.retrevo.com/support/Yamaha-YST-SW320-Subwoofers-manual/id/320bh340/t/2/

See page E1 regarding placement and safety.

http://www.retrevo.com/support/Yamaha-DSP-A595-Amps-manual/id/319ag821/t/2/

Page 44 - read about "humming".

If you have hum on the sub, is it there with and/or without the input cable attached?

Disconnect the input(s) and see if it hums in the absence of an audio source. A bad audio cable shield or unwisely-routed audio cables will allow entrance of unwanted signals from external power sources, magnetic fields, even dimmer-controlled track lights. Sometimes, simply reversing the orientation of the ac power plug can eliminate humming.

Check for a power source nearby. Speakers are notorius for hissing (60 cycle hum) when near an electrical wire, outlet, 'zip-strip', amplifier or tranformer. It sounds like this might be likely in that it is only one speaker that is misbehaving.

Iassume you mean you hear the buzz independently of the audio program - simply connecting the cable causes the buzz?

If tanything in the mix is powered from different AC sources you may have a different ground potential. Sometimes manipulating the orientation of one or more ac plugs will solve hum problems.

It sounds like you are describing an earth loop problem. I won't go into detail in this post, but try an isolation test first. disconnect everything from the reciever except the sub and try connecting say a BATTERY powered mp3 player or cd player to minimise connections to the electrical mains earth. you could also isolate things by taking your sub to a friend's house and trying it on their system.
If it is an earth loop use a process of elimination to find out which two pieces of equipment causes the earth loop. then apply filtering.
you can buy earth loop isolation transformers for about AU$26 and I've used one on my sub myself. Theyhave RCA (phono)plugs on each end and they connect inline with the signal cable to the sub amp.

as for the thumping sound it might be the speaker protection circuitry cutting off the amp to protect the subwoofer speaker from damaged. This might be triggered if the earth loop sound is causing the sub amp to overload and clip.

Failing this there might be a dried out overheated electro capacitor in the amp circuit causing the hum. Hav a chat to your local electronics person, who should be able to spot it!
Hope this puts you on the right track
Happy Hunting!

Sounds like the hum might be mains hum caused by the failure of the power supply capacitor(s) in the sub. It/they will be the largest on the pc board. You will find all the details (needed to replace it) on them. If you find more than one replace both.

Most humming sounds in speakers is due to electrical currents or wifi signals nearby the speakers.

Do you have any electrical cables near the speakers? Do you have any wifi device near the speakers?

If so move them out/away and see if there is any difference.