Terible noise when starting

Every once in a while I get a terrible noise when starting. I thought at first it was the gearbox. It sounded as if the dog ears were going past each other. I have overhauled the gearbox with new springs.  Thoroughly cleaned the clutch etc. The tension test is about 240 in # which is on the low side, but once in a while, It is still doing the noise. I did notice that the dog ears do look worn and should be replaced, but could that be causing this problem? Could it be that the clutch slipping?

I don't think it is the sprag clutch as it doesn't kick back when It starts.

Any suggestions?

Ernie