Not the Dunlop one! Mine whines a bit when it's on, but most of the noise comes from the actual PSU itself rather than out of the speakers!
Diago 18v adaptor tips can convert 9v to 18v but I've had troubled history with them, first one lasted well over a year before it decided to become a 6v adaptor, I got a free replacement which died within a few days, the one after that played up also after a month or so. I ended up receiving one of the old models with a second SFT that I picked up here and that one is still going strong, so it looks like the older hand made jobs are faring better than the newer Chinese manufactured ones (although of course I could have just been unlucky!).
This one should be good although does not have a right angle tip: http://www.effectpowersupplies.com/18v-dc-regulated-power-supply-7-p.asp
There's an EHX one too, but don't get that as the polarity is wrong for the SFT: http://www.effectpowersupplies.com/18v-dc-regulated-power-supply-7-p.asp