My statement about the FS4000 shielding is only a supposition.
2 months ago, I had the opportunity to test it and I was happy with the results I've got. I didn't notice noise or streaks but I didn't really had time to tweak the scans to see if there was defects there. But I must also say that the unit I tested was also defective : FARE system was u/s.
In fact, I decided not to buy it when the user complaints started to spread.
I'm a user of Canon photo equipment : EOS-1s and some of these lovely big white tele lenses. But lets face the thruth : the FS4000 is a good product on the paper but its occuring defects, poor slide analyse performance and bad driver kick it out of the competition if you need a reliable scanner for serious work ( ie advanced amateur & pro ).