Sounds like a faulty speaker. The only software thing that could cause it is too much amp gain in audio controlling apps. Just for ruling out purposes, back it up using smart switch and perform a factory reset, if it is still the same, contact samsung for a repair / replacement
I have no affiliation whatsoever with O2 or any subsidiary companies. Comments posted are entirely of my own opinion. This is not Customer Service so we are unable to help with account specific issues.