I've replaced the front and rear plates of my BFL Single SC with special, professionally-machined plates designed by this guy:
https://bitcointalk.org/index.php?topic=277000.0https://www.bitmit.net/en/item/54944-fan-plate-set-for-bfl-single-scs#and I've noticed a definite noise reduction.
EasyMiner reports operating temperatures lower by 2-4 °C, which in turn means that the fans don't need to rotate so fast, which is another reason for the noise reduction, and as a bonus, the miner consumes less electricity.
All it took was removing four screws (you need a Torx screwdriver) and replacing the plates.
Yet, despite the gains, the machine remains a little too noisy, so I eventually bought a 5-meter USB cable and I am about to install the miner in the next room.