when I start my jcb backhoe I get a deep kinda grumble off and on for a couple minutes. Is that the hydraulic fluid just pumping through the system or can that be a sign of my pump going bad or what else could that be? After it warms up it doesn’t really make that sound anymore. All of my fluids are within normal ranges
Air in fluid, too thick of fluid, restricted suction filter or strainer?
Change the hydraulic filter. Then, cut open the old one and look for contaminates. As Tenwheeler mentioned , it has a strainer on the pump inlet line clean it. Hopefully both will be clean.