I remember that wisp of smoke in "Journey To Babel." I always thought it was because they were cauterizing something.
Yes, I also always thought the smoke was deliberate because of a medical laser or something. Such things were on the drawing board when the show was made.
As for TOS bridge noise, I was truly shocked when I first watched my brand new copy of the TMP-DE and heard that sound effect. It seemed SO appropriate and added greatly to the bridge scenes, Most of all, it didn't seen dated.