Hi everyone. I'm new to drumming and have recently bought some late 50s A Zildjian hi-hats (weights are 903g and 772g). I'm experiencing a 'hum' which changes according to the pressure I apply to the foot pedal. I've included an awfully shot video to demonstrate (sound up, please). Experienced drummers: is this normal? What might be causing it? Is there any way to stop it? Thank you in advance for your wisdom.