Yes yes, language changes over time. I've heard that mantra for decades and I know it. That doesn't mean there aren't language changes that aren't grating when they become fashionable (and hopefully temporary).
For me, "morals" being used as a crude catch-all application of "morality," "ethics," "integrity" or related concepts bothers me. Sentence example: "Maybe if society had morals there wouldn't be so many minorities in prison." 
An even more annoying otherwise-fluent-speaker modification I see is when "conscious" is used to mean "consciousness" and "conscience" interchangeably. Sentence example: "Single mothers on welfare that steal baby formula have no conscious." It sounds like they're saying the shoplifter is not mentally aware of their own actions, not that they're lacking sufficient "morals" to let their baby starve for the sake of Rules-Based Order(tm).
There's others, but those two come up enough recently, with sufficient newness, for me to bring them up here. Some old classic language quirks are so established and entrenched that even though I hate them, bringing them up would likely invite some hatemail and maybe some mystery alt accounts also sending hatemail after that. You know, because they "could care less(sic)" about what I think. 
I pronounce those th's the same. I honestly don't understand what you're talking about.
The unvoiced one sounds like compressed air, a hissing kind of noise like 'sssssss' but with the tounge touching the bottom of the top teeth.
The voiced one has a throat vibration like when you say 'errrrrr', simultaneously with the unvoiced mouth position.