From my experience as long as your error are spread about, it seems to be a reasonable/expected rate currently. If you have a spare hub it may not be a bad idea to separate your DMs from fans that may pull lots of energy/create lots of vibration.
Thanks CruzCoins. I think I'll move the fans anyway, mainly because I want to be able to more easily turn them on and off. If that also happens to reduce the error rate, then that's icing on the cake.
Otherwise I'll just keep an eye out on the error rate to make sure it's uniform and not rising dramatically.