My gut feeling is to ignore it as long as the car starts well (with no misfires afterward) and performs well.
I would use a catalytic fuel additive like redline to be sure you don't just have a minor injector/carbon problem.
We have found that delivery valve leaks internally in the pump will cause idle knocking. It doesn't seem to matter and the solution is fairly easy, but there is no way to know but to do it. Its probably not a DIYer job. The elements require a special socket to torque them (a retorque often solves the problem alone).