Yep, and there is it thanks to @Jeff_the_Coaster_Guy https://ogrforum.ogaugerr.com/...3#145015890418376733
Exactly what I suspected, a high pass filter in series before the speaker. It would block DC, but also would limit 60Hz before making it to the speaker.
With 40uF and and a guess of a 16 Ohm speaker, that works out to 248Hz cutoff.