L-101 "halftones" On C notes

[Spinetarian]

Looking to pick some brains on what steps I should take to fix this issue: an octave up from the middle C's (on both upper and lower) this C note on has like a chirp sound, instead of the full tone as every other key has...

[Twiggybush]

I would suggest testing all the tonewheels to see if one is stuck. It's fast, it's easy. Clip a wire to the back of a '8' drawbar and pull it half out. With the organ running, all wheels can be heard individually by touching your test lead to the solder tabs on the back of the generator. If you find a dead one trace the wire to it and give it some love.