Try plugging an Audessy mic into you phone and doing a frequency analysis with a spectrum analyzer app.Thanks everyone! Today I drove a return trip of a bit more than 30 minutes, so 1 hour in total without radio plugged in and subwoofer powered off. The ear pressure is much less! There really must be something with either the stereo or the subwoofer. I can try driving with stereo and without subwoofer to see if the problem occurs. My ears feel 'relaxed' now in the car instead of stressed out. My ear drums didn't pull back like usual.
I want to figure out what the problem is. Maybe my stereo speakers are too old? 15 years. I'm not sure what the problem could be, but I definitely want to keep my ears safe AND also hopefully enjoy my beautiful sound system as before.
Might help you pinpoint the problem.
You might just have ears that are particularly sensitive to certain frequencies. In the days of tube television, I could tell from anywhere in our not-small house when a TV powered up. The flyback transformer gave off a high-pitched whine that only I could hear.