Couple things. As long as its grounded to the microwave ground then its fine (yes even inside). If ur microwave is interfering with WiFi u have a serious radiation leakage problem (not good). U need an area larger than the wavelength of non conductivity for leakage so u would need a pretty big hole to leak microwaves.

I suspect what’s actually happening is the microwave transformer is leaking non microwave em radiation which is causing the interference (maybe via come capacitive coupling bs). Or ur microwave is busted and spitting out the wrong wavelength.

Either way I would test if a different microwave in the same location causes the same problems and if so its busted. If the WiFi antenna is near the microwave try moving it first.