Intermittent upstream noise: upstream transmit power pegging at 54.5 dBmV, OFDMA disabling, recurring drops

Hi Xfinity team,

I’m looking for help diagnosing an intermittent upstream issue that has been ongoing for several days and keeps resurfacing after temporary improvements.

Symptoms

• Internet becomes unstable intermittently (latency spikes, packet loss, brief dropouts)

• Sometimes improves on its own for hours, then degrades again

• Happens regardless of router (gateway is in bridge mode)

Environment

• Gateway: XB8 (CGM4981COM)

• Mode: Bridge mode

• Customer-owned router behind gateway

• Wired testing (Ethernet)

• No recent changes to in-home wiring or equipment

What I’m seeing in the gateway diagnostics

When the issue occurs, the modem consistently shows:

• Upstream transmit power pegged at 54.5 dBmV on multiple ATDMA channels

• OFDMA upstream disables and falls back to TDMA

• Large and rapidly increasing correctable and uncorrectable codewords

• Downstream levels and SNR remain excellent (≈43–44 dB, ~0–1 dBmV)

When things temporarily improve, upstream power drops back into the low–mid 40s dBmV and OFDMA returns — but the problem eventually comes back.

Why I believe this is a plant-side issue

• Sustained upstream levels at 54.5 dBmV indicate the modem is maxed out trying to reach the CMTS

• OFDMA upstream disabling itself strongly suggests return-path noise

• Clean downstream rules out in-home coax issues

• Behavior is intermittent and time-dependent, which matches ingress/noise in the plant rather than a constant wiring fault

What I’m hoping for

I’m looking for help reviewing:

• Upstream SNR and flap history over the last 24–48 hours

• Any return-path noise/ingress seen at the node or tap

• Whether this warrants a line/maintenance tech to inspect the tap, drop, or upstream path

I’m happy to provide screenshots of signal levels or error counters if helpful.

Thanks in advance, I appreciate any guidance from someone familiar with upstream/plant diagnostics.