I have an ATI All-In-Wonder 128. It's 4 or 5 years old. I capture mostly from a VCR and at times I record from my PC to a VCR. The problem is when the VCR is hooked to the cable TV there are horizontal lines moving up the picture when I capture and record. When I unhook the cable the lines disappear. I thought it was something with the cable, but they couldn't find anything.
When your cable is running through the VCR it becomes the modulating receiver for your cable tv. Often times the receiver in the VCR starts to fail or is low quality and cannot handle multiple frequencies at once. Sounds more like an issue with the VCR or the VCR is not set to AV rear or front when your exporting to tape from the PC.