[paddington]

you guys are thinking about the 19kHz stereo 'pilot' tone in FM radio. This isn't that, unless the tape is running VERY slow.. which isn't likely.

I'd say that is line noise - electrical interference on the audio cables during recording - or playback.

We'd need to know how it was transferred to WAV to be able to guess about that. If you can post audio samples of some quiet places in the recording, I can analyze it and tell you where it probably came from.