I don't remember the alarm I got but when that happens to me its either the low voltage supply or a servo amp going bad.....generally its the amp but the low voltage supply has caused it 1 time.
If its been happening since new they should've given you new amps. and tested the old ones. Small price to them.
The way I check it is by changing the servo amp for another, in your case move the Z amp to a different position and see if it goes away...then you know the Z axis amp is bad or going bad.