Occasional noise from speakers

I have got some Logitech z506 speakers and i just noticed a noise that comes from them. Its a pulsating noise that sounds like a faint helicopter in the distance. I also noticed this once with a bravo audio ocean. I believe that my power is the issue when i disconnected the z506 from the computer the noise still came and when i hooked up my phone the the ocean it was still there. What can i do to further narrow this down and what might i be able to do about this.

I have a apc backup ups but have tested going strait to the wall and no difference.

First make sure that no power cords are running right along any of the audio cords. Check to make sure all the connections are secure.

Do you still hear the noise if you plug headphones into the front right speaker?

To be sure it's not any interference, you could try moving the speakers to another room, away from any other electronics.

Yeah, it sounds like interference like fademaster said. Could be anything from power cords being too close to your audio cables, to poor shielding in the speakers internal amp, to your cellphone receiving a call/text or just communicating with the tower.

I tried again With my headphone amp. I had the noise from it even when it had no input. it disappeared when i went to the other side of the room. Next im going to try the outlet with everything else unplugged. I will let you know what happens.

Do you keep your phone near to the equipment?

My grandparents used to have this 2.1 Logitech USB setup. Whenever it was on it would pick up AM signals.

The radio source might not be localised.

When unplugging devices from power it immediately stopped after I unplugged my ac router. Further experimenting shows that when I move the antenna it increased and decrease noise. Looks like i'm going to have to re arrange my room again. Luckily I bought cat 5e when our radio shack closed.

Thanks for the help it did turn out to be radio signals.

I didn't know radio waves have so much influence on audio electronics :O. Glad to hear you found a fix.

Unamplified signals will pick up radio interference from various sources, including signals from the power going through power cords. Usually shielded cables are recommended for unbalanced audio connections, but most PC speaker systems don't bother with shielded cables.