I got a 70's dunlop wah pedal. Its all stock. Sounds amazing clean or with amp drive. But when i run clean and have my blues driver or big muff (germanium fuzzes seem to have a more subtle effect) it kindof does a harsh wistel of feedback when i go "toe down" for more than a split second. Is this normal of wahs. Is there a vox wah thats better about this problem.