Another one bitten by the bug
First thing I have measured, just because it's right next to me is the the ringing of my 3D printer's hotend PID regulator output. It has been mentioned voltages can get pretty high over there in RAMPS boards and boy, that is true. At around a 50-volt spike is produced when the load is switched off. And the real value can only be appreciated if you freeze the sampled signal and expand widely the time axis, as the spike duration is below 1us. I guess total energy is so small the MOSFET is not really damaged (as it has been sitting there for three years now without stop working). Values in the order of micro Joules seems to be safe as the STB55NF06L is avalanche tested and the single pulse avalanche energy is 300mJ.