Well, the right gcode commands can over-ride a lot of the printer default settings. It could be you've got configuration issues in the slicer. When does it squeal? When trying to home? That's governed by HOMING_FEEDRATE in Marlin (at least in older versions I'm familiar with).
You could always post a small gcode file that has the z-axis issue for one of us to take a look at. It'd also be helpful to know how you went about adjusting the trimpot for the Z-axis stepper driver...