VHS sound problem on playback

[Barquentine]

Does anyone know if a VHS cassette casing has any tabs or dimples that affect what the VHS recorder detects and plays back?
My holiday home video (transferred to an ordinary VHS tape) plays fine on the video in the lounge, but is completely muffled on the video in my bedroom. My bedroom video plays all other videos fine. The remote has an audio input button which switches the display between L then R, then L&R together, then both off. When I put other videos in both L&R appear and I get stereo sound. When I put the holiday video in both L&R disappear - like the VHS casing is defective in some way (although the video downstairs works just fine with it).
I'm trying to transfer videos to DVD (& the DVD recorder works fine upstairs, but I've no idea how to re-configure the cables downstairs because we have Sky and dozens of other things hooked up to that TV!).
Please can any of you clever Answerbank people help me?!!

[rojash]

Have you tried adjusting the tracking?

[Barquentine]

Hi, yes I've tried the tracking up and down but makes no difference. I can't understand why our other video plays the sound without problem. And it's odd that the L/R (left/Right) audio out indicator on the display disappears only when I put this one tape in. My first thought was that some tab on the casing must be missing, but comparing it with other tapes - it looks all intact.

[rojash]

Early VHS tapes had a single, VERY LoFi audio track which ran along the edge of the tape. Later VHS recordings had HiFi stereo which was merged with the video data, and extracted during playback - to retain backward compatibility the lofi edge of tape audio was recorded as well. It sounds as if when playing upstairs, the HiFi track is not being detected for some reason. Are both VCRs Hifi? Was this video recorded on one of these machines?