Hi there! I recently bought a Zoom B3 multieffect, and is really really awesome! But there is something strange about it. If i play connecting the B3 directly to my headphones, there is a buzz that stops if I touch any metal part of the bass (LTD D6, active) or the B3 itself. But, if I play connecting the multieffect to my combo amp, then from the combo to my headphones, it won't buzz at all. Is this a ground problem?