Description of the problem (What does it do? What does it not do?)
Pedal creates a loud high pitch whistle when engaged. Replaced the transistors and had the same result. The pitch of whistle changes when the gain/level knobs are turned but always exists. Q1 seems microphonic when knocked.
List any modifications/component substitutions
Zero mods. Used Siliconix J201 through hole from reputable source.
If applicable, did you hard-wire the 3PDT switch or use a Bypass Board?