I am getting the very common hum when I switch to series. Everything that I have found here and on GbL says the problem is because the control cavity is not shielded. Is this something that I can do, if so how do I do it? Do I just need to take it to a guitar guru? I haven't noticed the issue that much until I changed the battery before the last gig. I hum was real noticable and I had to switch it to parallel between songs.