knocking or tapping on outgoing calls

I had an Android (Google Pixel) and experienced knocking and tapping sounds for over a year. T-Mobile store changed the SIM card. It didn't help. This went on for more than a year. Then I got an IPhone. The issue continues. T-Mobile did try a number of methods, but nothing helped. They kept closing out my ticket (which took forever for me to get them to agree to open to begin with. I did have one kind technician (I don't think he was an actual technician) who checked in with me a number of times. NOTHING CHANGED. I finally realized on my own, that it only seems to occur on outgoing calls. So, I call people, the knocking begins, and I ask them to call me back…..and no knocking. It's not my tower. It happened even in New York. It doesn't happen on every call, but I'd say 90% of calls. It's absolutely horrible. I stumbled upon a group online Apple community, where a number of people are complaining about the same issue. They think it's an Apple issue, but they ALL HAVE T-MOBILE. Since I had the issue with both Android & IPhone, I KNOW that the problem is with T-Mobile. I am utterly disgusted, and dissatisfied with the service.