I realize this is probably the oldest and most annoying question out there, but is there any way to eliminate or even diminish the amount of buzz and hiss you get out of passive pickups short of buying 'noiseless' ones? I'm going crazy with this hiss here!

Guess you'll have to dig up some information on how to fix that. You can definetly eliminate the noise. I've only had the problem in a P/J setup where the J pickup buzzes depending on where I stand, that is a common phenomena due to the number of coils or something. The fix is to replace the J with one that has two coils.
If its that bad, you must have loose wiring or something.

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