Why does my radio stream drop out nearly every time I listen?

When I'm listening to Sirius online, I am always having my stream drop out without warning. It's always replaced with what I was listening to ten or fifteen minutes ago. I assume that it's buffered some of the content, and it's pushing me back, but why is that? I have so many problems with listening online that I'm considering giving up on Sirius. I used to have a car, but that died recently, so I only listen online. Is there any way I can get a more reliable stream?

I'm on a Mac, if that matters.