Hi I've had a venue di for a long time but I've never used it on stage because it has quite a grounding hum whether it is powered by 9volt or grounded power source. On top of that it makes a terrible popping sound when I mute it to tune, and if I accidentally bump it it makes a banging noise as if it where a raw ontact pickup. Any ideas, suggestions on where to get it work on, or how much it might cost out of warrantee?