Speaker feedback

Hello, so yesterday my speakers decided to stop working properly so I picked up some logitech z-2300's from a guy on craigslist. So I got it all hooked up and plugged in and I'm hearing some feedback from them.

I have my xbox hooked up to my computer, hdmi to monitor and rca's going to a 3.5mm for line in speaker control, I had a 3.5mm splitter so I could have headphones as well.

When I have the RCA/splitter plugged in I get feedback, when I have the splitter only I get feedback, when I just have the speakers plugged in there's no problem. I tried plugging the RCA into the line in on the back, and the speakers on the front input I'm still getting feedback.

What would be the reason for this?

Motherboard: http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Should I maybe get a sound card?

http://www.newegg.com/Product/Product.aspx?Item=N82E168...