Used non-technical terms that mean something different for you. Yes it could be an aeial tap or someone in an appartment. For all we know, it could be a bad power supply on the cable modem or bad modem itself. Especially if the gound block is not gounded, I've see a few fried cable modems that act flakey and drop power. I've also seen an amp cause the same issues. It doesn't hurt to recomment checking a few basic things. Otherwise my last footnote applies, call Comcast.
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