some suggestions from another site:
1. A hydraulic leak in one of the hydraulic lines or pump itself could be causing the hydraulic pump to run, but it does not have enough hydraulic fluid pressure to operate the slideout.
2. A bad hydraulic valve could again cause the hydraulic pump to run, but not enough fluid is getting to where it is suppose to, to move your slideout out.
3. A bad hydraulic pump. The noise you are hearing could be the pump trying to start up. Since you are hearing a noise when you press the slideout switch, I am not going to suggest that you check for a blown fuse.