A new noise has started coming from the hydraulic pump on our press. The pump used to run fairly quietly, but now, after 20–30 minutes of operation, a humming sound and slight vibration of the housing occur. I checked the oil level—it’s between the marks—but the oil is already quite dark. The pump was serviced about eight months ago, so I’m not sure if this is due to wear and tear or another part of the system. What would you look for in a situation like this?