The Enterprise Incident - S3-E2
Audio problem: During the scene where Kirk is talking in the briefing room, the director was obviously not pleased with how James Doohan said his lines. Due to budget constraints, instead of re shooting the scene, they simply replaced Mr Scotts dialogue with another one. You can see it since at one point his lips are completely out of sync, even on the remastered edition. (00:06:40)