29-09-2019, 08:59 PM
It is very strange that you have exactly the same noise from both boxes, that said I have not come across a box which has been converted to CR gears that is completely silent, but your Nippy box is original so???. Some of the CR conversion sets which have been through my hands have not been the most accurately cut and one set was sent back it was so bad. I almost every case I have had to regrind the bore of the 1st motion shaft, as supplied the bore seems to be tapered from the new gear being shrink on and sometimes very rough from spigot bearing wear. I did manage to quieten down one very noisy set by running the gears in on a lathe with very careful application of a fine grinding compound. Layshaft's and bearings can be horrendously worn, if this happens the gears drop further out of mesh than ideal so it is not just end float that you should be looking to address. I have corrected this with either a better layshaft or had the shaft reground and made new bearings. Hope this is of help and gives you a few ideas to investigate.
Black Art Enthusiast