We had some electrical wiring that was overheating and burning/melting the insulation around the wiring. It was a super weird smell that the best description we could come up with was a mild, but gross fish smell. It would start 5-10 min after turning on the light that the wiring ran to and then take 30+ min to dissipate after turning off the light. We had to have an electrician track down the failure point and replace the wiring.