Cable modem: Downstream Channel Change minutes after reset, speed slows dramatically
I have a CM400 (Netgear) cablemodem, which has worked fine for the last several years. In the last 24 hours, however, I've seen it slow to a crawl. Resetting the cable modem - whether I do it, or Xfinity does it remotely - results in fast speeds for about 10-15 minutes, at which point it then slows to a crawl.
Looking at the CM400 modem status, I can see that the "Acquired Downstream Channel" shifts in frequency when this occurs. Here's the summary:
Immediately after reboot:
Downstream Channel 723000000 Hz Locked, QAM 256, Channel ID 41, Power 4.3 dBmV, SNR 38.6 dB
Speeds as measured with web-based speed tests @ ~100 Mbps down.
10-15 minutes after reboot:
Downstream Channel 663000000 Hz Locked, QAM 256, Channel ID 31, Power 4.7 dBmV, SNR 38.2 dB
Speeds as measured with web-based speed tests @ ~2 Mbps down.
Any ideas what may be going on here? Thanks!