Strange light buzzing/hiss when headphones are in headphone jack
 

I have my mac laptop in an adjacent room to someone's bedroom, & I use head phones to listen to music so as not to wake them while working with content on my external hard drive.

I notice I have this when my external hard drive is plugged into my hub & turned on, what is it? is it serious?

I dont this sound when my hard drive is not turned on & running.

This is standard electrical interference. Something, somewhere, is not as well shielded as it should be or could be. This is very common on tightly-packed devices, especially when anything in use is cheaply made. In this cases, I'd note that most laptops use somewhat budget-grade sound cards, and Apple is no exception.

Serious? No.
Just annoying, at most.

is there anything I can do about it?

this seems odd since I see apple laptops and computers used by DJ's & others in the music industry.

Not really.
Try better external speakers or headphones, maybe.

I second all the information given by the gentlemen above. I would also suggest that you try higher quality headphones (if you don't have high quality already).

Is your external drive running directly off your Macbook, or is it plugged into the wall?

If it is running off the Macbook, try a different port, then try different cables (USB or Firewire).

If it is running off the wall you may be receiving interference from your house's wiring. Try another wall outlet to see if that helps. If not, try the same setup in another building. Preferably, a business that was recently built and has higher grade, modern wiring.

... in case this wasn't clear enough -- kaliree means for testing.
..... Not that you have to move into a new office building -- hahaha! -- Just wanted to clarify that.

That's actually a good idea. :)

~~~~~~

If it does turn out to be power-related, then a good UPS may be able to filter it.
Sossity, are you using a CyberPower or APC UPS (uninterruptible power supply) -- a.k.a. a "battery backup surge protector" brick?

Oh! Good catch. :D