Loud touch tone sounds during phone calls

This problem is due to misidentification of loud, clipped input audio that is near a DTMF frequency and also has a harmonic component that is close to one of the other DTMF frequencies in a valid pair (e.g., 1209 Hz and 852 Hz for keypad "7" in the US).  The harmonic can be due to room reflections, bad microphone preamp, etc., but is usually due to DSP artifacts from overdriven ("clipped") input from the microphone.  However, you can get _both_ causes at the same time when using a speakerphone, since most of these use adaptive gain control and/or dynamic range compressors that can clip before padding the input.

Given such a signal, some stage in the chain is misidentifying these as distorted DTMF tones, and trying to clean them up by substituting them with clean DTMF tones-- but normalized to DTMF line level specs, which are quite loud.  This is great for making sure that voice-maze stuff on the other end can get clean keypad signals when you're on a bad connection, but is entirely inappropriate for voice conversations.

I'm not sure exactly which stage in the chain is causing the problem, but I don't think it's the handsets.  If I had to guess, I'd say it's the cellular base stations, but it could be switching equipment further down the chain.

One thing it is NOT is some kind of third-party listening nonsense.  This is DSP code that isn't quite as smart as it probably should be-- that's it.  Modern wiretaps are read-only and do not interfere with the signal being transmitted at all.

My friend from a few states away and I talked on our cell phones about a half hour ago. We were also both experiencing what sounded like someone constantly pressing the keypad (we eventually ruled out either of us doing it). We also both have normal male voices (nothing female-like or remotely high in pitch which I've read can sometimes both emulate and trigger DTMF tones). At least during part of the conversation it appeared as if the tones occurred during our pauses (and not while we were talking), but it's hard to know for sure. All these years later these phone carriers don't seem to have a handle on this yet. I haven't completely dismissed, however, that it might be something else entirely. 

Regarding "modern wiretaps are read-only and do not interfere with the signal being transmitted at all", I do not know enough about this technology to say one way or another, but tell me if this sounds plausible to you. Some people might think this is crazy, but I am telling you this happened for a fact. Maybe there is a logical explanation other than someone taking control of my computer, but I haven't found one (nor did I know this ability existed without my authorization and/or loading specific software). AT&T is my ISP (via DSL). 

This is a screenshot of a spreadsheet I had just started working on using my Macbook Pro laptop computer. My wife and I were the only people in our home at the time. I had just created the first line of my spreadsheet and paused for a few minutes to do the dishes. My wife and laptop were on opposite sides of our living room, and because of the way our kitchen & living room is orientated, neither were ever out of my sight the whole time (and my wife never went near my computer). 

When I came back to my Macbook, I saw someone had typed "Hello you watching". I have redacted the first line of the spreadsheet because it was private and inconsequential (the cells were just showing brand/model information about something). No other information had been typed into this spreadsheet if anyone is thinking somehow I inadvertently populated this. I assure you that did not happen (I wouldn't even type like this). The red triangle is just a note I added after the fact. As you can imagine I was a bit startled discovering this. Do you or anyone else have a logical explanation other than someone hacked into my computer? I know former CBS reporter Sharyl Attkisson also had someone take control over her computer in a similar way. If this can happen with my Macbook tied to the internet, despite assurances we've heard to the contrary, might people be hacking our cell phones as well? If someone is willing to make it obvious that they're on my computer, wouldn't they might similarly make it obvious they're listening during a phone call? 

Again, if there is a logical explanation for it, I welcome it. I would rather not live my life under the assumption my conversations, internet access and other aspects of my life are being monitored without my knowledge & consent, but this happened a few years ago and I've had to live with this assumption ever since. 

Im in England...and its 2020, i had this happen for the first time ever today exactly as others have described it dominated the full phone call! I have the Samsung galaxy s6 edge ive had it about 3yrs and its never happened before.

I am in Canada, and my mom also gets these beeps while in conversations on her phone. It is a LANDLINE so not just cell phones yet when I looked up about dtmf talk off they say that only effects mobile cell phones and voip which she does not have and lives alone and her hand part she talks into does not have any buttons as they are only on the base of the corded phone itself. 

This is relevant as it seems this is more than a network issue and not just AT&T customers experiencing this. Yet .. no solutions. 

She is convinced someone is listening to her calls and pushing buttons to interrupt her conversations.