John Deere 250 skid steer

I got a friend that has a 250 JD skid steer 06-07 model I think. There s a light coming on that says "restricted filter". He put on a new filter and the light still comes on, cleaned the 2 small hydrostatic screens light still on. Whenever the oil warms up it has a occasional slight squeal to the loader hydraulics. What needs to be done next? Thanks in advance!!!

John Deere 250 skid steer