I've been working with a PAM8302A analog audio amplifier from Adafruit and added a second order low pass filter (2 x 470Ohm resistors and 2 x 2.2uF capacitors) to get rid of some of the audio feedback that occurs when the analog mic (Electret condenser mic with MAX9814 mic amp) is near to the speaker.
I've noticed that when I am testing it out and have the speaker near my ear (less than a foot away) for even less than a minute then my ear starts to bother me even when the audio from the speaker is not very loud. I do have reasonably sensitive ears and pay attention to when they start to hurt and don't like loud concerts etc because of that. I would classify my hearing as pretty normal.
I've used an app on my phone (an instrument tuning app, Tunable) to detect the frequencies from the speaker and I've noticed that when I turn the amplifier on and off by connecting or disconnecting the power (and not changing the SD signal prior to shutdown) that there is a 10kHz burst of noise. I sometimes hear a little crackle but the audible noise doesn't seem like it could cause a problem because it is not loud.
I am considering getting an oscilloscope to search for frequencies from the audio out.
What could be the cause of the ear issue or how can I troubleshoot it?
*** Edit to add spectrum analyzer screenshot. ***