Sometimes, the music can blend in with the dialogue if one is hard of hearing. That aside, it's not always hard to notice general episodes' volume mixing and when one or two episodes are out of sync.
On top of that it's worse when the music is flagrantly bad (in terms of tonal quality and/or its trying to pull emotional strings, especially sobbing maudlin sap. It's too often forced, especially if the script's content doesn't deserve the accentuation. It feels too robotic.
It doesn't help when, at least in the 1960s, all this was done by imperfect human hands and not by perfect clock-cycle computers with pre-set settings and the rest of it. Or who keeps changing them for editing different shows.
It also doesn't help when all sorts of shows use wallpaper music to increasing quantities and effect for affect. It's worse nowadays, even bombastic - the more bombastic usually means a weaker story, but the trend started in the 1980s and has rarely gotten better since. A good script and solid acting do more for a story than music or visuals ever could. As a design instructor kept telling his students, "less can be more".
In the end, the TV stories are still about the dialogue most. The background incidental music should never compete against it, or be so loud to replace it. It's just at the point where clunky dialogue isn't as bad.