I play on older fender jazz which I cannot put down or trade in - in other words, I will play this bass as long as I play the instrument..... However........the bass consistantly goes sharp as it sits in it's stand - especially on breaks of 15 to 30 minutes. The bass has done this for years. No temperature/humidity change seems to be doing this. It does it from the first set to the last and has made me wonder for years what is going on. Anyone have any ideas??