My advice is that you not get it fixed. If you do, it will unmask all the other interior buzzes and rattles.
As ingenious and superb as the Volt drive-train is, they went totally "chevy" on the interior. Everything seems to be assembled using relatively loose spring clips, so on bumps and rough roads especially, my interior sounds like I'm riding in a wicker basket. I dislike rattles and buzzes so much, that I suspect this is my last Chevy. I just hope something like the Volt drive-train finds its way upmarket by the time I'm ready for a new ride. But not as upmarket as the ELR -- that was a bit too far upmarket. Maybe other automakers will get into the act. But I believe it would take them awhile to catch up with GM's drive-train engineering.