ibanez classic metal soundtank cm5

i just got this pedal second hand..it works but when i pluck a string its makes a sound but then keeps getting louder until i mute the strings, it does this on all strings..sound like maybe something isnt grounded. maybe i need a new instrument cable.. i pluck the strings and it keeps getting louder with volume or distorion or it peaks, im not sure how to describe but somthings wrong..i tried fiddling on the amp and the pedal.. any sugestions, thanks