Yep, Start pulling reverse pads and work your way from the head end out. I had one just last week that took out 1/3 of our modems. I tracked it down to a RV park. An RV with a RF setup for television and rear view monitoring with a DVD and satellite setup in the mix was blowing all kinds of noise into the system. It took about 4 hours to track down.
This is CABL.com posting #155076. Tiny Link: cabl.co/mOvo