cm400 modem drops internet connectivity

I have a cm400 modem that periodically drops the internet connection with Comcast. The ethernet and upstream lights blink for several minutes, eventually re-establishing connectivity. The modem log indicates the following timeout messages occurring over the course of about 10 minutes: T3, T3, T4, T3, T2. Then a connection is made. This happens a couple of times each day. I've checked all cable connections and they seem fine. Is this a problem with the modem (less than 1 year old), or with the connections (mine or Comcast)? Thanks.