Panasonic VCR random audio problem

Good Day:

I have a Panasonic PV-S7670 VCR S-HIFI(1998). It works great and the picture is great. However, I'm having a problem with the audio recording mode. When recording a video tape, sometimes the audio portion of the broadcast does not record properly. And, when we playback the tape there will be no sound, or it will be very very faint, and then at times the sound will all of the sudden come on and be normal, and then immediately go off again.

This does not occur all the time, sometimes the audio works perfectly. Other times it does not at all. The problem is with the record side of the taping process, (playing back on a different machine does not alter the problematic audio).

During the recording and playback process, we notice that the HIFI indicator light on the front panel flashes on and off, which is an indicator that the tape is having a recording problem, other times the HIFI indicator light stays on, and the tape audio recording is perfect.

Any help would be greatly appreciated. We like the machines very much, and it seems a shame to replace it over such a minor problem. I'd like to repair the machine myself if you can give me some advice on what part may need to be replaced.

Thanks for your help
Best Regards,
Rayko