Super Hard On
Did this whistling just start or has it always been there with this set-up? If so, try putting those two pedals thru the loop instead of the front. If not, Im leaning toward microphonic pre-amp tube. One way to test for the tube option is to take the back off, with nothing plugged into the input take a wooden pencil and lightly tap the glass of each pre-amp tube. If you have one going bad you will DEFINATELY hear the difference.