http://www.tvshowsondvd.com/newsitem.cfm?NewsID=4901
According to the specs, the audio is English mono. That couldn't be anymore wrong, considering the 4th season was the first (and only) season to air in stereo. The intro even said "In Stereo, where available". The theme song and background music stood out even better than it ever did. I hope it's just an error on Universal's behalf, and the DVD set ends up being stereo. Although it was just 2.0 stereo, it's still better than plain ol' mono, and plus, it's always best to have it the way it originally aired (reruns are also stereo).