Have you tried unplugging everything?
Plug in modem, wait, plug in router, wait, plug in extender and wait for it to find GPS.
Is it always the same person or everyone tells you it sounds like crud?
Everyone says I sound like crud. My husband isn't having the same issue, just me. Just moving around the room and it gets worse. I tried unplugging and replugging everything. This most recent call says I sound OK. I will wait and see if it stays that way.
I was thinking more along the lines of the SIM card being old or faulty, it's now you connect to the network. I'm guessing you've tried some basic trouble shooting, but if not:
Turn off Wi-Fi, power down, remove the SIM card, wait a couple minutes, reinstall and power it back on.