Dial Tone buzzing noise that breaks through into speech

[NAROBS]

When using my main landline telephone, I'm now getting a near constant noise on the landline handset earpiece. This noise sounds like  a muted dial tone. The noise interferes with hearing what's being said and saying things to others using the phone. People I've called/callers are reporting hearing it too. Its happening on incoming and outgoing calls. It seems to go away when I use handsfree.

Handset is a  18 month old BT Decor 2600 with call blocking.

Reseting the phone to default values, plugging the phone into the master socket and operating the phone without its electrical transformer make no difference.

The noise is there when using the BT Line Test facilities, but goes away when "Handsfree" selected.

Also noticed that when call blocking is selected at phone setup, that "Ring back" on BT Line Test 17070 doesn't actuate the ringer, though the unit registers an incoming call on screen. From memory, this didn't used to be the case. Is this  the new normal ?

N

[imjolly]

Have you tried using a different phone to see if the noise is still there and eliminate a problem with your current handset 

[NAROBS]

Yeah. I tried a  plain vanilla Decor 2200  in the master socket, same deal, although the "Breakthrough" wasn't as noisey.

There have been at least three occasions this year when the BT Smart Hub 2, which operates from the same master socket,  has gone down early in the morning (02:00) which haven't subsequently shown evidence of firmware updates to the hub and where the hub Event Log just shows a sudden loss of signal, . . with  restoration  of signal about half an hour later.

Taking a guess, I'd say someone has being doing work on the line. 

Swapping the handsets between the base units did improve the issue  slightly,  . . with the Decor 2200 handset operating from the Decor 2600 base unit, the noise went more muted, high frequency, but it was still there.

Again, just using the Decor 2200 handset and base unit together, the noise was still there , muted, more high frequency, but still there.

I'm wondering whether a line fault has provoked a fault in Decor 2600 handset and, because its persisted, caused permanent damage to it ?

[NAROBS]

To add

I've just used BT Test Line (17070) and found that when using the handset with the mute button engaged the noise on "Quiet line" goes away - as said ealier ditto  the "Hands-free" button. Does this mean that the problem is being caused by some sort of feed-back the microphone in the handset -either sonic or electronic. 

Would such an effect be caused by excess voltage on the line causing electronic leakage ?

Might the voltage have been turned-up to clean-up VDSL signals on the copper side of the FTTC circuit ?