Vintage Synth Repair

So how come some pedals 'pop' when I turn them on, and some don't?

Are there classic keyboard Wah's out there, or do we just use guitar 
ones?  I understand that a keyboard wah would perhaps cut different 
frequencies (a broader range), but all [guitar] pedals are 'full 
range', as in they don't discrimate against the lowest frequencies, 
right?  Is there a company out there that makes analog effects for 
keys, or are we stuck with guitar pedals?

Just thought I'd open up a little discussion...(I'm sick of my 
current pedals for my Rhodes)

-Alex