1971 Duster 340 10" front drum brakes - what other Mopar brake drum hubs will fit?
this noise is quite common in the two wheeled world where drilled rotors are the norm. the cause can be anything from a symptom of the floating caliper design, improper sequence on install (centering hub or wheel), debris on the rotor or pads. or, as some have hypothesized, air or gas being trapped and released in the holes during operation.
i'd go back and check the install with a critical eye.
fwiw, when i had wilwoods on the street they were always a little grumbly. after they were properly bedded and has some miles they were better but nowhere near what i'd describe as quiet.