Frequency-specific ingress at 789 MHz, likely line/plant fault, all purchased equipment ruled out

I have a persistent ingress problem that I've isolated to the line itself, and I need a line-maintenance/network investigation, not a standard level-check visit.

The fault: Continuous uncorrectable codeword errors concentrated on the downstream channel at 789 MHz (accumulating tens of thousands per hour), with correlated T3 ranging timeouts. Every other downstream channel is clean. All signal levels are in spec (downstream −1 to −3 dBmV, SNR 40–43 dB, upstream 41–43 dBmV). The error rate is worst during morning/daytime hours which is consistent with LTE Band 14 (788–798 MHz) ingress entering through a shielding fault.

What I've already ruled out, by direct testing:

• Removed a splitter (fixed a separate low-signal issue) — 789 MHz errors persisted
• Replaced the coax jumper with new RG6 — persisted
• Moved the entire setup to a different room on different interior wiring — errors followed
• Connected directly to the entrance/grounding block — persisted
• Swapped to a completely different brand of modem — the 789 MHz errors reproduced identically

Because the fault survived a different room, new cable, direct entrance-block connection, and a different modem, it is not my equipment or interior wiring. The ingress is entering at or before the point common to my unit, the drop, ground block, or shared building wiring. This requires line maintenance to investigate for an ingress/shielding fault at the tap, drop, and ground block, and check for a compromised connector or unsealed enclosure near 750–800 MHz.