The music was really out of whack in Season 5 (ABC Season 4)
Watching the original ABC broadcasts of some of these particular episodes, I noticed that the music was really sounding off key and lower-pitched (anyone else noticed this?). I'm guessing it was because by this point, the reels that the music cues were on were getting worn out from being used so much, and it was time to change them.
They would do exactly that in the next season.