They want to come out and "fix" my internet. I ask if anything's broken and they say no, but its preventative. I've asked what's it suppose to prevent, and they cant tell me. I ask them to stop calling and immidiatly I am having connectivity troubles. Seriously? It's hard to assume thats just coincidence. Is there any explanation?
Comcast is calling you because they have detected an issue with your connection. Let them come out and fix it, it's free. If you don't, they may eventually disable your service until repairs are made since your issues may be causing problems for other customers. Let them fix it before it gets worse. It won't get better on its own.
Most likely you have some bad physical connections someplace that are allowing the ingress of unwanted radio signal (noise) onto the cable system.
If noise was detected on the line, why wouldn't Comcast communicate that to the customer. That is what a company with good customer service would do. I still say scam call.