I'm not sure what's meant by "ache" here. An "ache" I'd probably just try to work through, and I would supplement with bicep work. It might be worth mixing up the order of exercises as well. Try varying grips to see if that helps.
I have what may be a similar issue. I have a piercing pain in my left bicep that shows up at some point in most any back routine I do. The pain I have is at the lower end of the bicep into the brachioradialis. I've quit doing direct bicep work as a result. (Today, just for kicks, I tried reverse curls again with only 40lbs. and gave up very quickly.) Anyway, my pain is significantly worse on wide grip pull-ups compared to neutral grip. It tends to not bother me when I do row work, but I stick to neutral or supinated grips. I do not think I have an obvious strength imbalance. I'm going to duck and post some stats. I'm 5'7" and about 150lbs. The last time I did curls I could do 50lb. dumbbells for about 8 reps. These days I do rows of about 200lbs. for 8 reps. And I can do neutral grip chins for 5 reps with 80lbs. attached. I did 15 reps with 50lbs. on the dip belt today. And I bench about 215lbs. for 10 reps.
I tried total rest for awhile and things got a lot worse. I tried doing bicep work for a bit and it seemed like it was getting a bit better, but then one day it was as bad as ever.
Any suggestions on how to fix this would be much appreciated. In the meantime, Zep, try varying grips to join me in the "if it hurts, don't do it" club...