Wierd smell in apt

So let me just say that I'm borderline OCD clean. I clean 2-3 times a week but I'm always wiping something down and organizing cause I'm kinda messy at times.

I noticed a weird slight sour/trash like smell in my living room/kitchen. Kind like that period where the trash is starting to smell but it's not bad enough for a trip to the dumpster

Chalked it up to trash initially but it it kinda persisted and cleaned my bin just incase, and seamed to be comming from the fridge/freezer

• No expired food, dairy, fish etc. My fridge/freezer is clean but I cleaned it again just to be sure. Got got my hands and knees and checked under as well. I even Through my eggs away that seems fine but what else was there? Freezer has salmon in it but itz frozen. Cleaned that out too. It kinda comes at goes though

did a another deep clean Poured bleach down thr drains which I do a lot anyway Mopped floors all that stuff

I started getting wiffs in my room now though

I'm thinking it's the HVAC or maybe the drip pan in the fridge

or worse it's something in a neighbors unit.