It's just normal operation. Contact arcing generates wideband "noise" that's propagated through cables, capacitively and inductively coupled to other circuits, radiated and received again.
Thinks you can do:
- reduce contact arcing by RC snubbers, varistors or freewheeling diodes (the latter with DC switching only)
- reduce succeptibility of your mcu circuit to switching interferences by good ground layout, power supply bypassing, filtering of external connected signal and supply lines by series resistors or ferrite beads and parallel capacitors or voltage limiting diodes