toolndye_dave's counterbalance call is spot on ??that's probably the #1 missed diagnosis for new noises. Easy check: look at the nitrogen pressure gauge (if you have one) or do the static balance test. With the press at TDC and drive disabled, the slide should hold position or drift up very slowly. If it drops, your counterbalance is low.
Adding to the diagnostic toolkit ??one trick I use for localizing noise source: get a long screwdriver (or better, a mechanic's stethoscope for $15) and touch the tip to different components while someone jogs the press slowly. You can isolate whether it's:
- Ball screw (put stethoscope on the nut housing)
- Gearbox (on the gear case)
- Motor bearings (on the motor housing)
- Gibs (on the gib adjustment plate)
The character of the noise tells you a lot too:
- Grinding = bearing or gib issue, usually metal-on-metal
- Whining that changes pitch with speed = gear mesh or belt issue
- Clicking/popping once per rev = ball screw ball return, or a cracked ball
- Rumbling at BDC only = counterbalance bottoming out
The 40 SPM specific thing is interesting. If it ONLY happens at 40 and not at 35 or 45, that's almost certainly resonance like raj_pm said. But if it happens above 40 (gets worse as you speed up), that points more toward a mechanical wear issue that only shows up under higher dynamic loads.