Intermittent Static noise on phones

[perrymcgrew]

We are a healthcare facility.  For past several months we have had several complaints from users that calls are often full of static.   We are running CUCM 12.5(1)SU8 and the phones are primarily 8811 running current firmware.   We have replaced phones, handsets and tested all data cable connections. Can not find root cause.

The issue is intermittent, but when it happens, they state it is all phones in the nurse station have the static.   It happens on both internal and calls to PSTN.  Of course, when I visited the floor, I could not reproduce it.   But a nurse did record a video and we could hear the static.

Looking for ideas / suggestions on possible causes or how to find the root cause.

Thx - Perry

[Leo Laohoo]

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@perrymcgrew wrote:
they state it is all phones in the nurse station have the static

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Do you have any 4- or 8-port switch (preferably PoE-capable) around?

This problem only affects the nurse station and nowhere else?

[perrymcgrew]

All phones are connected to Cisco 3650-48PD switches.   Plenty of PoE+ power is available -- typically several 100's of watts.  We use Voice Vlan macro and QoS tags are honored.  

The facility has many floors but the issue reported only occurs on a few of the floors.  Only the Nurse Station and employee offices (i.e Manager, social & recreational staff) have IP phones - typically 8 or so. Users report Static on "all IP phones" when it occurs.  The Nurse Station is almost always occupied by staff.  

Thx - Perry

[Leo Laohoo]

Try this:  Temporarily install a 4- or 8-port PoE (fanless) switch nearest the nurse station and connect those phones to that switch.   Then pose the question:  Has the static remained, slightly better or completely gone.  

Whatever the answer, use the temporary switch and observe the uplink to the 3650 for any line errors.  

[perrymcgrew]

Unfortunately we do not have any of those switches.  Our Cybersecurity policy would not allow us to place a switch in an open / unsecured area.

I have run TDR tests and taken our Fluke cable tester to these locations -- no issues found.  

Perry

[BradMarkel93582]

Static is most often introduced in an analog connection of the call.  The handset cord itself, the connections to the phone or handset, or a headset connection.

The speaker phone could be faulty.

Wireless headsets can create static for a few reasons.

Analog phone cable in the path of the call could be faulty.

I'd start with identifying an example call and looking closely at any transitions between an ethernet packet to analog connection.  More unusual causes I've seen are circuit trouble with PRI circuits, too many DECT wireless headsets in one office, a bad phone firmware release.