Are you using a speakerphone function on the handset causing a feedback loop?
Have you tried a different handset (borrowed from a friend, family member, neighbour etc.) to test if you have a handset issue or a line issue?
Welcome back to the community and thanks for taking the time to post here on the forums.
I’m sorry to hear of the issues that you’re having with your landline at the moment, is your line connected via the wall socket or your router?
If its by the router, are you able to reboot your router and check to see if that makes any difference?