How do I know if there is water in my fork
The XCRs are very simple forks and unless specified don't have an oil or air damper so very user friendly. 

It is possible that water has got below the dust wipers but this is generally unlikely. 

The mechanism for a XCR is a sealed lock out unit and a coil. You should simply be able to drop the lowers off the fork without disrupting anything else to check them out for water and to ensure there's plenty of grease to protect the spring and other internals.

The 'whum' could be the stanchions being a bit sticky moving through the wipers but not much else I can think off.