Mysterious Interference Hum?

Hello all!

I have just bought a beautiful set of Logitech Z-560 4.1 speakers. I'm so happy with their crisp, percussive sound & RAW POWER.

EXCEPT FOR A BLOODY ANNOYING, CONSTANT INTERFERENCE HUM!

When plugged into my Soundblaster Live! 5.1 they pick up a shockingly annoying interferance hum - they're almost UNUSABLE!

If I unplug the jacks the hum almost dissapears. If I move them through the air around my case, the interference increases slightly as I get closer to my 2x 40gb HDD's.

I have tested the speakers with other devices away from my PC and no hum.

Bizzarely, the hum is not as bad if I run an extension cord from the other end of my house to the speaker system - the hum increases again when the speakers & PC are on the same powerpoint!!

This one has fooled me. Could it be a problem with my Soundcard? Perhaps it picks up interference from my HDD's? Are HDD's known to cause interference?

Do you have any ideas?
Thanks!

AMD 1.4G
256M RAM
GForce 2 Pro
2x 40G HDD
19" Philips 109P Monitor
Win ME (heh heh)
Logitech Cordless mouse

"Ok, is it plugged in ?"
"What do you mean 'IN?' "
"Oh... God...shoot me..."

Hmmm, a hum, probably at 60Hz. This can be caused by not having the speakers pluged in all the way, or a line near the audio cable. If it's internal noise, it could be caused by the CD Audio cable, have you tried removing that to test it?

<font color=blue>You're posting in a forum with class. It may be third class, but it's still class!</font color=blue>

Thanks for your help guys. I've been too busy with work to even turn my speakers on lately, but had a chance this morning.
I discovered this;

I changed the powerboard & all power cables.
* No change. BIG HUMMM.

SO I played with the speaker & PC power cables & discovered this;

* When speakers NOT connected to PC & PC UNplugged from mains, no hum (well, der)

* When speakers Connected to PC & PC unplugged from mains, no hum

* When speakers NOT connected to PC (plugs lying on floor near PC) & PC Plugged into mains, SLIGHT HUM

* When speakers Connected to PC & PC Plugged into mains, BIG HUM! - The PC does not have to be powered on & running.

So I tested further with my other system, which is an AMD k6-400 with a Diamond MOnster Sound MX400 Sound card. I placed this system in the exact spot my system was.

* NO hum whatsoever in any situation. (WHa!? WTF?)

SO I brought my system back into the room and replaced the sound card with the Diamond from my old system.

* Exactly the same problem as in original situation. So supprisingly, I don't think the Creative product is at fault (IT DOES HAPPEN!)

NOw, as suggested, I have done some reading about ground loops. The logitech Z-560's don't have a ground plug. Waht would this mean?


BTW, I have tested with & without power to the monitor & it makes no diff.

So, as it doesn't matter if the PC is ON - only plugged into the mains - I am wondering now if this problem could be the powersupply? Could it not be grounded properly?



"Ok, is it plugged in ?"
"What do you mean 'IN?' "
"Oh... God...shoot me..."