If you notice it going on, and others do also, there may be an issue worth getting checked.
My mother had similar problems, I can't remember the conditions that can cause this (I am sure there is more than one) but hers was related to 'nerve deafness'.
She also had high frequency hearing loss (she could not hear watches beep, for example).
I'm only saying it because it sounds similar, I am not a professional, just making conversation. But it is worth checking out, especially if you think it is getting worse.
