In Internet Explorer, type in 192.168.100.1, hit the signal tab and see your modem levels, especially the upstream power level. If it's at or near 60, the modem is at threshold, and this will cause it to cycle. Removing a splitter on the cable feeding the modem will make this number go down.
This is CABL.com posting #162874. Tiny Link: cabl.co/mQxa