Lower Spray Arm

[LD78]

I have  3 year old dishwasher that started making a screeching type noise suddenly, when the wash pump kicks on.  I suspect something entered the pump somehow, as it sounds like something rubbing or grinding.  I tried to figure out how to remove the lower spray arm to access the pump.  I thought that the gray thumb type  on top was removable, but no matter which way I turn it does not come out.  Any ideas or at least how to get the lower spray arm off so I can get in to take a look?  The parts diagram was of no help.  

Model Number: GU2500

[sparky823]

Turn your screw in the middle of the arm clockwise as you hold the arm. It should come off---the arm will the screw/nut doesn't.

I have a Kenmore with the same arm I think as yours and this is how it works.

Hope this helps.