Dahdi/wanrouter abstracts the analog channels into 64kbs TDM channels in all cases, power supplies work at 50/60 Hz, it’s thus not feasible for a PSU failure to cause cross-talk, again look to your wiring 
In my case it was on the DC power, not the AC. I could hear the audio when I connect a test-phone to the DC rail , The whole system went into the junk pile the same day; some 10 years ago
Right, but if you’re hearing audio on the DC Power, you are not using a TDM connection. It’s still a problem with the house wiring. For this to be an issue on most installations, I’d think you’d have to be using a channel bank of some kind.
My buttset has a polarity warning that tells when when I’ve punched a pair down backwards. If the reversed line goes into a 2-port module, it can cause all kinds of strange audio problems. In addition to crosstalk (which I’ve experienced on a couple of installs), it can also cause feedback that one of my customers refers to as “spaceship noises”.
One other place where I’ve done this to myself is by cross-punching a pair of lines. If you install the ring from line 1 with the tip from line 2 (and vice versa), you might get a problem like this.
Another thing to remember (and which was checked) was that you can have crosstalk at the near end or the far end. If you phone company couldn’t find it, it’s probably near-end.
Cross-talk is an analog problem - it won’t happen in the digital side.
Beating a dead horse here. I did hardware support for a long time and was a lineman before that. When this happens it is always wiring and often a crossed pair. The way things are designed the only place cross talk can typically happen is in the wires barring some board design flaw which would affect thousands of boards.