Could be a line problem in your house. I would check all of the connections between the modem and where it enters the house. Insure they are clean and tight by opening each one and then putting it back together. Do not over tighten. If you get TV from your ISP also, check those fittings also. Eliminate any dead end connections (nothing attached). Did anything change before the issue started such add/remove a TV? If you replace any RG6 fittings, get good quality fittings, not those cheap big store gold ones. If you can not find it, you may need a service call from your ISP so they can check the signal quality.