I picked up a set of pickups from ebay for my peavey cirrus. After installing them, I notice a very high pitched sound coming through the amp (sound kinda like that subtle high pitch noise that comes from a TV when its on, but more noticeable). This only happens when the pickup blend pot is somewhere in the middle. It goes away if it is blended completely to one side or another. I checked and double checked the connections and they are good. I also tested each pickup individually by desoldering the V++ line on each pickup and testing the other and the blend works fine (changes volume of pickup with no noise). What can be the issue?