Weird rising oscillaion when pedal is by-passed

[pqt_bach]

Hi everyone,

I have this wierd problem when the guiar and amp are connected to a pedal I've built (high gain-ish FB diode clipper) in by-pass mode the second I plug in the power adaptor to the jack - I get a fain but audioble whine for a couple of seconds. Also at maxxed out gain there a faint "crckle" sound with the initial attack on the strings...
I have no idea what this could be. Any suggestions?

Thank
P

[MR COFFEE]

Power supply funnies. They can oscillate on startup or loading, if not properly designed, which is quite common in diy designs.  Loading and adequate output filtering help... if that's why it's oscillating.