Ana you are so right about BBC in particular. I have seen letters in newspapers about this. The background music and other effects (eg a trotting horse clip-clopping, or a motorcycle engine) are too loud, and the sound engineers do not bring up the voices, many which mumble anyways. A whisper is totally lost amidst props being touched moved by the actors, the dialogue volume needs to be enhanced. This is about poor directorship as well as slopping scene engineering and editing with after-effects.
I work on 3D modelling and am in an animation workshop and these are big issues. So it's not about older people being deaf!