Case DX45 3 point "shimmy"

[DH44]

I have a 2009 Case DX45 with HST, cab, FEL, etc. It has 400 hours on it and has developed a "shimmy" in the 3-point lift. It doesn't matter if the attached implement is super-heavy or not, but when it's raised there will be a slight lowering, then the lift raises, then sinks, then raises. It doesn't seem to be RPM-dependent. The hydraulic fluid level is good and the fluid is clean. Any ideas?

 

[MuleMn]

The pressure relief valve on the 3ph lift cylinder may be bad. Mine is doing same thing. They call it porpoising. I have found that if the hitch is raised under load ,then partially dropped, it sometimes quits. That leaves me to believe either a valve sticking sometimes or trash. I will probably change both valves, be cheaper than dealer experimenting. Have you found what is wrong with yours?

 

[DH44]

Not yet. I'm taking it in soon for service. Are the valves easy to get to?