It's probably dying from Bad Capacitor Disease. The highnpitch noise is a typical symptom, and so is the frequent rebooting. Note that this is a power circuit failure, and as such a serious fire...

tpPLC utility, individual device settings or "extended settings".

That is exactly the symptom - traffic on PLC interferes with the DSL signal. As described above, make sure your DSL/phone wiring - both the loose cables and the wiring in the walls - is as far away...

@viktor0704 First of all, for improved signal quality on the PLCs, plug your other devices INTO the PLC not besides it. The PLC adapters contain noise filters in the power passthrough, so that your...

@SaltzyBros_ DSL uses a frequency range where Powerline operates too. So in a house with poor wiring, when phone and power wires are in close proximity to each other, the strong Powerline signal will...

@tim9800 So just join the 3rd adapter into your existing network by manually entering its device ID code. Open tpPLC while connected to your working pair, select "Add Device", enter the 16-letter ID...