Power supply problems..????

[col]

I'm still having trouble with this;

http://www.diystompboxes.com/smfforum/index.php?topic=60956.0

The circuit works perfectly with a battery over about 7.5v to 9.5v but whenever I attach a regulated 9v power supply it just makes a farting noise when I hit the strings. I have tried other supplies as well so it's not his specific one. I am connecting the batteries externally with a dc barrel connector to the dc in socket so it's using exactly the same connections as the power supply. I have tested the power supply at 9.7v and the circuit is drawing 25mA which is within the spec for my unit and the others I've tried.
I have tried connecting a 0.25w 9.1v zener across the supply which works fine with the battery but overheats immediately a power supply is attached (why does this happen when it doesn't with the battery?). I also tried a 2200uF cap across it to see if that made any difference but it didn't. The power supply is regulated and produces no noise in any of my other pedals so building a 9v regulator circuit won't make much difference. I don't like using batteries because of their environmental impact and would much rather connect to my power supply but this one really has me stumped. I really want to use this pedal as it sounds much better than my Boss chorus.