The Mysterious Metal DB Box

After so many years in this line, its not easy to be surprised anymore. But today, at the a customer's place, I was stumped. This was because after laying an Earth cable, my technician could not get a proper reading from the meter. (I asked him to do this otherwise he would not have done it. He would just pack up his stuff and go off). And so, the next day, I dropped by to see that the problem was.

This is very strange. There IS voltage
on the metal DB Boxes.

I am not sure what is on the other side
of the wall bit what I got here was 25
volts DC. And if everything is correct,
there should not be any voltage at all,
AC or DC.

Finally, after taking the boxes out, I discovered that
the voltage came from the screws, just like my Boss
said. Its a very long screw and after replacing it with
a shorter screw, the problem went away but there
is still some trace voltage.

And we might have top shift the two boxes an inch
to the left or right since these plastic wallplugs are
impossible to remove.

Funnily enough, at the same time, one of the customer's line was out and so, we had to lay a new cable for them. And then, we were faced with another mystery. The line has a nice tone when we tested it at the bottom floor. And it was the same at the customer's floor. But once we punch the line in, the quality went out of the window. After much testing, we could not find any problem until the last cable connection to the system via the metal DB Box. Once we nailed the problem, everything was OK. And so was the mysterioys voltage! But I cannot discount this due to coincidence as the voltage did come from the screws. My only though would be that some device was not switched on at this time when we went to measure the voltage.