Why does my computer audio input and output get interference on a regular basis?

I am the owner of a Macbook running OS 10.5.8. About half a year ago, the audio input and output jack for the laptop ceased working, and after a little research I discovered that I must have somehow accidentally bent the jacks out of shape. In order to remedy the situation, I did some more research and purchased a USB to Audio Adaptor. I converse with friends regularly on Skype, and it worked fine for a few months. Then, my friends started informing me that my voice starts to sound like a robot every 15–30 minutes, and the only way to fix it is for me to log out once, close and open the laptop, and log back into Skype. It’s definitely not my headset, and it doesn’t seem to be native to Skype (I’ve tested other applications) so I’m thinking that something is interfering with the USB soundcard– does anyone know what could be causing this?

Recently, the interference has also started happening when I am listening to other people’s voices as well, causing their voices to sound garbled. This only happens when it is a two-way audio conversation, and never when I am just listening to music, or watching a movie.