I really love shellac-coated bar wrap, but I'm experiencing something odd this summer and last. When I put weight on my handlebars, I'm hearing a sort of creaking sound. Seemingly like all bike noises, it's a little tough to nail down exactly where it's coming from, but it's definitely associated with the bars or stem. I checked to ensure the stem and bars are adequately tightened. Like I always do when I pull a stem or seat post, I added a touch of grease (I'm fanatical about those two spots in particular.) When those didn't clear up the issue I grabbed my Sherlock Holmes cap and pipe and sat down to ponder things a bit. Here are the facts:

• This is intermittent. The creaking is only apparent in the summer during the hottest and most humid conditions. In Missouri, that means I only hear it when both the temp and humidity are in the upper 90's/90%.
• It's only apparent on the bikes with cotton wrap coated with shellac. Different stem and bars on each bike, so nothing common between them. On the other hand, I have the same bar and stem on two bikes: one with shellac and the other with cork wrap. The cork wrap bars are silent.
• When we rejoin the rest of the world, in terms of climate, the sound goes away entirely.

It doesn't seem to be causing damage, but the noise is driving me a little nuts. Anyone else experience this? Is it possible it's unique to shellac coating? I'm all ears, folks.