windshield fluid

Today's washer fluids contain isopropyl alcohol as their antifreeze - so that's the typical odor - but I don't know what "very weird" means relative to that. In an Audi shop this is usually dispensed from large containers as it's used across the range. A little overfill will often evaporate near the normal cabin ventilation pickups so there's a good chance upon fill that some odor would get inside for a few cabin air changes. If you've had a recent service this is entirely possible, but if your service was in January and you're just now getting an odor, I would rather suspect one of the tubing connections to your hood or pump has come loose or broken (really unusual) and when you use the washers, this leak will also get into your cabin vents. This might also explain why the level has dropped off so relatively quickly. The top off is a normal thing for about every service of the car.

I noticed the odor since when I first got the car in September.

I notice the antifreeze smell inside the Q3 too. I've never smelt antifreeze inside a car before my Q3.

Antifreeze (propylene glycol) has no odor. Isopropyl alcohol has a very distinct, sweet aromatic sharp smell - not unpleasant. It is common as a solvent in perfumes and colognes too, but is masked by the perfumes themselves. You would most likely encounter isopropyl alcohol around a doctor's office or some of the hand sanitizers (main ingredient) that you find; or maybe recall your mom wiping a scrape with a dab of it.

Beware of Audi dealers trying to hand you the bill for Rainx clogging up the jets and pump...I told the dealer to show me the placard on the wiper reservoir that says I can't use Rainx...no I'm not paying $550 under warranty for that...Audi you can work that out with Rainx and find out why the Rainx product I have been using for 20 yrs all the sudden can't be used in my Audi.