Dell/Mac Headphone Output: Annoying Hissing Noise

[djquikcompton]

There is a constant hissing noise coming from my headphone outputs in both my Dell laptop and iMac. This noise varies with the type of headphones I use: the better quality, the more noticeable the hiss.

Does anyone know what is the cause of this problem and whether getting a external usb soundcard will help?

[where02190]

The source is the cheap soundcard, and yes a decent ADDA will remedy the issue.