Wurlitzer distortion (huge pops) at high volume

[osheroff]

Hello,
Been servicing my 1971 Wurli.  It's got a nasty distortion problem that appears both in headphones and speakers, on all keys, but only when I crank the volume nearly all the way up.  Here's a link to what it sounds like:  https://www.dropbox.com/s/lajfuhcldhqke7v/Wurli%20Distorting.m4a?dl=0.

Anyone got any tips or thoughts about how to proceed troubleshooting?