It was a total mystery to me! So, I finally went back to my friend Rick at Quality Hifi and was happy to discover that my NAD was still under warranty...a relief as I do not have the spare ash to upgrade to my ultimate dream: a Bryston preamp, obviously! It took two trips to the importer the Audio Product Group and a few weeks (during which I reinstated an old Sansui preamp, that I duly cleaned and pampered before putting it back in service) and I finally got a call from Rick, to tell me that, although I was French, APG and NAD had agreed to replace my unit with a brand new one!. Well done! And I am happy to report that this new unit sounds much cleaner than the first one even before the noise generator incident. So now I have some time in front of me to save the 2000 odd dollars needed to access my next upgrade - btw, I will accept all contributions toward that goal!