I swapped pickguards on 2 of my strats. One I still have to trim some extremely long pickup adjustment screws so it hasn't been finished yet. The other now hums in 2, 3, and 4. Perfectly silent in 1 and 5. It never hummed on the other guitar. I copied it over wire for wire. The only difference being the one that hums was a double humbucker and is now a 3 single coil. Since it's a Strat, the pickups were already mounted and only wiring had to be dealt with to the jack and grounding. The single coil pickguard had one more ground than the humbucker pickguard. I screwed it into the bridge pup pocket as the first had it. I soldered the long ground to the trem block and made sure my jack solders were good and solid. Why would it now hum in the middle 3 positions, if I followed the reverse of taking it off?