If you have another modem, try it to rule out the modem's fault.
Try switching splitters to eliminate that.
Check every connecting point and ensure the connectors are screwed tight.
They technically can install a high pass filter on the tap, although I don't recall if it will still allow your modem to lock or not.
Try switching splitters to eliminate that.
Check every connecting point and ensure the connectors are screwed tight.
They technically can install a high pass filter on the tap, although I don't recall if it will still allow your modem to lock or not.