You don't mention a model but does your exhaust hood have any of the following: screens, inserts, filters, catch trays, hand-removable baffles, or any other device that appears to serve as collection media for vapor condensate. If so, have you removed and cleaned them according to the manufacturer's recommendations?

The reason I ask is that my range hood has metallic filters that I take out every 20 hours or so and run through the dishwasher. That and some 409/Windex on the underside keeps the grease at bay and my nose untroubled.

On the other hand, my nose has not won any accolades for sensitivity, so there's that.

I know this is a really old post but did you ever find a way to get rid of the smell? Searching here as I‘m having the same issue. Almost brand new Zephyr hood that I haven’t had any issue with until we seared tuna last night. Now inside the hood itself smells of burnt grease. I’ve washed the baffles/drip tray again, and wiped the grease from the outside of the pipes that house the fans but the rest of the inside appears clean and free of any residue.