This seems to be a bit of a thing with A7's and 10's. Muskrat is right with the cause but some seem to make quite a audible noise while others are silent.
I had the same thing with my 51' A7 and spent many, many hours trying to work out exactly what it was. I am not sure if some have more clearance in the meshing of the gears or maybe there is some very slight variation with the teeth profile but for some reason some, like my A7, make quite a audible click. Mine has been doing it for about ten thousand miles now with out any problem.
Certainly double check everything to make sure it is not the generater chain or anything touching anywhere but if you cant find any problem then I would let it be. If you take the timing side off and kick the motor over you will be able to hear the noise, then remove the idler gear and it will stop.
Richard L's advice for listening is good, I use a screwdriver. Stick the handle in your lug ole and put the tip on the area of the engine you want to listen to.