Thanks for all the messages - what a fantastic response!
Since posting the query I found a minidisc site mentioned in the earlier thread with a FAQ page that seems to cover the problem. The site is at www.minidisc.org/index.html and the ref to the "problem" is as follows:
Mechanical Noise and Recording Level Hi there, I have a couple of months with my R-70 and it works perfectly. However, it does make noticeable mechanical noise, now let me tell you why. Also seen or treated as an energy-efficient feature, what this great MD does is that it reads 40 seconds of audio in only 5 secs approx., so if you listen carefully you'll hear this noise every 40 secs more or less. This allows it to be practically skip-free, I haven't noticed any skip while jogging or driving around town.
I have checked this out on my own recorder and it seems to fit. I have been to a session tonight and just used a cheap mic that came free with a PC and playing it back now I have to say the results are excellent.
Given that I only bought it this week it is not fully road tested but for £99 (previously £199 and then £149) I have to say I'm more than just a little bit impressed.