I've been playing my old German plywood a lot lately after a long hiatus. I keep the action pretty low and have noticed strange phenomena with the fingerboard. In a matter of days, the very end (towards the bridge) tapers up towards the strings, on some days nearly touching them, but always producing a buzz. Then within a few days, it'll correct itself, becoming nearly parallel (with proper relief). The board is solid rosewood, the bass bar, bridge and sound post are all fine, there's no separation anywhere on the fingerboard/neck and the change only occurs in the last six inches and is consistent across the base, no twist at all. It remains in tune as well. Granted it was brutally cold over the past few weeks, with little to no humidity and yesterday when it corrected last it was in nearly 60 degree F with 100% humidity, but the bass is in the same spot it has been in my dining for 20 years and I never noticed this before. I'm more curious than concerned since I only play for myself at this point in my life and don't see anything serious happening to it. Is this is normal behavior? My MusicMan StingRay changes wildly with humidity, but this part of the DB is under no tension, it's just hanging out in space. Thanks in advance for any thoughts or information.