Analogue systems

hi everyone!  i wish i was joining this group just for the fun of it 
but, alas, my rs100 is misbehaving and i need your help :/ first up, 
the output has become quite noisy i.e. about 20dB noisier than all 
my other modules. i also noticed that when the cutoff is high, 
turning the resonance pot makes a crackling noise; this gradually 
decreases as i reduce the cutoff. i got the filter second hand but 
i'd be up for paying Bob to fix it if that's cool with him? or, if 
any ladder filter gurus reading this recognize the symptoms and 
think it's an easy job i could attempt it myself... what do you 
think?

thanks for listening,

thom