Oscillator Modulation switch -- problem? (w. video)

Hi guys -
Wondering if something is slightly in need of calibration on my Model D. When I activate my Osc Mod switch – even if my mod wheel is at 0 – I notice the slightest drop in pitch. Has anyone else noticed this? Any suggestions would be most appreciated. Also, if interested, I’ve attached a video.
https://youtu.be/GxpJyc_OpwY
Many thanks as always!
Paul