I replaced caps C103, C300L, C300R to no avail. Also tried the resistor bypass that member poty mentioned, no effect.
However, I think I may have stumbled upon the problem. One of the resistors that I had updated (Clarinet resistor update) a few months ago, R310R, had a poor solder job on one of the joints.
I discovered this because the sound from the left channel woofer was crackly. Like the sound one gets from poor contact. Probably didn't notice until now because I been listening for the hum with my ear right up against the woofer.
Oddly I always suspected the left channel sounded lower and not as full as the right.
Any how, at first I reversed the interconnect and the sound moved to the right channel. I figured it was a bad interconnect cable, but after swapping interconnects with another pair, it was still there. Then I started to look for suspicious solder jobs on the board and resoldered that one and now I can not perceive any hum from my normal listening distance. And the volume on the left channel is now louder and more distinct and clearer than before (specifically the lower region). I only hear some hum now when I crank the volume past 12 which is way beyond my listening level. Than you all for your help.