Pardon if it's a naive question, but I know nothing about electronics. My 2011 Gibson Thunderbird is making a crackling sound through the amp when I move it certain ways, and sometimes if I run my fingers down the strings. If I rest my finger lightly on the metal part of the guitar cable that protrudes from the output jack, it does not make the sound. The issue is not in the cable, as it does it with several of them. Electronics and pickups are all stock. Somebody suggested to me that it could an issue with grounding. I'm not sure what that could be. Any thoughts on that or other suggestions? Thanks in advance for any help.