Vinyl composition effect on noise floor

So here's a curious thing I noticed today. Red vinyl is noisier than black! Ok, that's not true exactly, but check this out. I have a record that's half red, half black. I noticed after cueing up the record but before the music started that there was a distinct increase in the level of background noise when the stylus traveled into and through the red half, then a decrease when it went back to the black.

So, what would cause this? Because it's the same record, everything about the two halves must be the same... same master, same stamper, same pressing equipment, same packaging, same cleaning before I played it, same stylus in the groove, etc. Everything, that is, except the composition of the vinyl itself. Now, I know full well that color has nothing to do with it; I've got several very quiet colored discs and several noisy black ones. But I hadn't considered before that the makeup of the raw vinyl itself could be this important to a quiet background. Makes me want to get more info from pressing plants about how they source their vinyl. Thoughts?

Here's a video of the record spinning so you can see for yourself. Please excuse the poor quality, and turn up your speakers. http://vimeo.com/24946684