Is it new?
Known issues if near a 4g mast
https://at800.tv/faq/can-get-filter/ May help you
It's like the old days when you had to put suppressors on the electrical equipment in the car to stop interference on the car radio.
I would guess it's a combination of old equipment.
Do family phones cause the same interference if they text or call within your home? If not, I would be looking at changing your phone.
If the same happens if anyone else uses their phone then possibly the problem alluded to by @adamtemp64
Hey @Florence76, I was wondering if either of the suggestions above helped you understand what's going on better? Do come back and update us on your progress please, it'll be very interesting to know what was causing this and how you solved it 
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