After putting on a screen protector and the lens protector, my sound was just fine, but it suddenly became absolutely terrible — extremely distorted, as if something was being overdriven — as soon as I put the phone in the case.
After reading your reply, I removed my lens protector, and that did indeed fix my distortion problem. It continued to work properly when I put the case [which I had thought was the problem] back on afterward. Then, just for an experiment, I also put the lens protector back on, and the sound is still good.
Maybe the lens protector just needed to be moved a tiny bit? To just not be exactly where it had been? I don't know.
I just picked up an A53 for an upgrade for my wife. Added a screen protector and also the lens protector and put the phone is an Ottorbox (the light one) .. After getting the phone up and running I too noticed terrible sound from the speakers when playing music or videos. It was distorted and almost like the speakers were blown. Once I removed the Lens protector and only the the Lens protector as suggested here, the sound was perfect. Thanks for adding this issue. DO NOT install a "LENS" protector