I gave it a second and third wipe down and it seems to be pretty much resolved. I think you may be right SFD. Maybe it just had some aluminum dust and/or bit of grease left on it.
Yeah, when I sand an empty hilt, I give it a good cleaning by running it under water and wiping it down. Obviously, not an option with electronics installed.
When you have electronics installed, it can take a few good wipe downs to get it all off.