intermittent cable modem resets caused by signal drop

July 20th portsmouth RI -I have been frequent modem resets for about 2-3 weeks, started about 2-5 times per day, now 2-5 times per hour.  I call support, they say: nothing is out of the ordinary.  they say: your modem is 4 years old.  they say: we could visit your house but if no trouble is found you will be charged for a service call.  

I buy another modem exact same model they sold me 4yrs ago. C3000-100NAS

July 24th afternoon install new modem - no resets for about 2 hours of usage, not watching the majority of the time - off to bed.  

July 25th Morning 7:30am rebooting constantly - called support they will said a tech and I have to wait another 2 days for them to fix their problems.