Should this be happening?

I have an X-Fi Xtreme Music and I just noticed that noises from other peripherals travel through my headphones. For example, I can very clearly hear the keys being pressed on the keyboard or clicks of the mouse through my headphones (Audio Technica ATH-A500s), and much louder than I would if I didn't have them on, so it's obvious that the noise is traveling through them (plus the headphones are closed air anyways). Even more obvious is that if I have my microphone plugged in, any noises are picked up by the microphone and come out of my headphones with no application involved in the process. I can say something and I'll have almost an echo (very small delay) behind me coming through my headphones, yet I have nothing running that would record any noise or anything.

If this is a problem, and I'm assuming it is, is it the sound card's fault? The headphones'? Or could it even be my motherboard's?

Nevermind, I just switched slots from the bottom one to the second to bottom one and it's not happening anymore... so either the last PCI slot on this mobo has something wrong with it, or something about the card touching the case in a certain way was causing it it looks like.