Check the following:
1) play in the rear wheel (side to side), you may need new hub bearings
2) check your RD hanger to make sure it's straight
3) check your chainring bolts... I just recently checked ours and they were loose! This was causing a clicking noise in the small chainring, and going up steep grades.
I am banking on the hub... I just replaced all (6) bearings in the rear of my solo bike, it was pretty easy.
If none of this works, I say take Butcher's advice
