I'm taking a reading off the output terminals of a home bass amplifier (Monoprice SMA-400) that has a consistent/stable squeal right around 1800 Hz and finding something I didn't expect and don't understand on my DMM readout. When on VAC function, I get 0.1794 VAC, and when on mVAC function, I get 416.38 mVAC. I expected these to be consistent; i.e. either 179.4 mVAC if VAC is the basis, or 0.4163 VAC if mVAC is the basis. What am I missing?

Separately, my DMM (a Fluke 289) has the capability to measure AC frequency, and when I select that function, I get a 0.0000 Hz reading. Perhaps the voltage is too low for it to measure? The speaker is making low but very audible noise... I would have expected to see some sort of signal frequency.

Thanks in advance for any guidance.