Careful with this, you might be doing more than just flexing your tensor tympani muscle, you might also control the pressure inside your ear.

I can do both of these. The latter is rather dangerous in the long term, although in the short term it does reduce the perceived volume quite a bit. For some reason when I was a kid I preferred a negative pressure in my ears which deformed my eardrum. I still do and I concisely need to remind myself to reset the pressure back to normal.