Readymix, thanks for mentioning humidity. As I read the above posts I thought " and what about humidity " and there you were. I sometimes use a vaporiser in the vicinity of the turntable, which is outside of the listening area and also a small spotlight. In my long audiophile years I've heard differences, which I related to both temp. and humidity in all mc's I ever owned
What temperature is your cartridge?????
When I worked at Adcom on the Crosscoil high output moving coil we discovered that we had to measure frequency response and tracking at a particular temperature. If it was warmer the cartridge ( ALL CARTRIDGES) tracked better and were brighter and on a cold New Jersey morning they sounded dull and wouldn't track for beans. Install a lamp next to your turntable and small themometer. Never go below 72 degree F. You can literall fine tune a cartridge by heating it up or cooling it down. It has to do with the compliance of the rubber used in mounting the armature.