Some BFL Single units make a rattling noise. This is in the majority of the cases caused by the smaller fan (enclosed in a copper/silver heatsink) that is touching the case. One very easy solution to fix the problem is to
insert 4 screw washers between the bottom standoffs and the bottom side of the PCB, in order to increase the headroom between the fan and the case. I myself fixed 3 of my 10 units this way:
I can sell you some washers since I have plenty extra. Email me at
m.bevand@gmail.com. I can mail (US only) 8 washers (enough for 2 singles) for 1 BTC.