Home audio & video: It's snowing in my bedroom (on the TV)

It's snowing in my bedroom (on the TV)

I have 3 TVs and analog cable. I have the drop coming into my house then it goes through a 2-way splitter. The splitter routes to my cable modem and to a 6-way splitter (only 3 cables connected to outputs) in the structured wiring box. While it sounds like this may lead to problems, it has worked well for the 3 years since my house was built. All 3 TVs have had great signal and picture until a few days ago. One of the TVs suddenly has a horrible picture. The lower the channel, the worse the signal. For example, channel 5 is terrible and covered in snow, but channel 55 is watchable. This happened suddenly, it wasn't a slow degredation.

The two other TVs are still great, and the cable modem is still raging fast (6-7Mbps). I've replaced the cable from the wall to the TV, and that did not make a difference. The cable inside the wall is not going to be easy to replace if that's the problem, so I want to exhaust all other options, first.

I'm getting digital cable this Saturday. What are the chances that the digital signal will be good enough to that jack to hide my problem?

Thanks for any help you can offer!