Ironically I heard the squealing sound from my black MSR+ that came with my 861v6 for the first time the other night and thought that it was an odd noise. It was the first time I had ever noticed it so I guess you need to either have acute hearing or just get your ears close enough to the remote to hear it.

Now that I have read this thread, I realise I am not alone.

#1: 8000s, 5500HC, 8000s, 861v8, 800Dv4, HD621
#2: 6000s, 6000C, 5000s, 6000s, 568.2mm, 598DP, 511
#3: 5500s, 5000C, 5000s, 561, 800v3, 518