Hello,

    If you volume knob on your guitar is open but you are not playing (allowing volume to come through) then this could be reverb/delay trails or feedback.  If you have it set to tweek a particular effect this could be happening as well. 

    If this is not the case you should try a reflash of the unit.

  Pod xt Series: Factory Reset, Reflash, and Firmware Updates

  http://line6.com/community/docs/DOC-3827

   Please be sure to award Helpful and/or Correct points to community members who respond with helpful or correct answers, and close out the ticket as “answered” if your situation has been resolved.

Glad to hear the reflash worked for you.