I have never heard of this with a wah specifically (just a guitar and amp is enough in a high RFI environment ). I am guessing that the filter on the wah somehow exacerbates the effect; if it is inductor based that might be why.
1. Try moving the entire chain (guitar > wah > amp and everything in between) to a different location (e.g. another room in your house) as well as orientation (which direction everything is facing). If that helps then take it back but rearrange it (when I had RFI interference I could usually eliminate it by turning myself so the guitar was pointing another way. Also the same rig would have the problem in the living room but not the bedroom across the house.
2. Build a faraday cage in/around your jam room (;p)
1. Try moving the entire chain (guitar > wah > amp and everything in between) to a different location (e.g. another room in your house) as well as orientation (which direction everything is facing). If that helps then take it back but rearrange it (when I had RFI interference I could usually eliminate it by turning myself so the guitar was pointing another way. Also the same rig would have the problem in the living room but not the bedroom across the house.
2. Build a faraday cage in/around your jam room (;p)
