What is causing grain?

I do not make colour prints with the RA4 process, but I still use colour film. I always have bleached and fixed for longer than the times suggested. The 6 mins recommended is extended to 7mins for the 1st film in a fresh 500cc mixes, extended by 30 seconds for each film following and never use the 500cc solutions for more than 6 films. Whilst not eliminating grain it has reduced it significantly. This the same with any manufacturer's chemicals

have you printed the neg? when scanning, I find that the monitor can show a lot of grain, but when printed it does not show as much in the final print