Apologize if this is a re-post, but I've been unable to find anything answering this question under these particular circumstances. The car is a 2007 A4, 2.0L with 51,000 miles.

After I've driven my car on the highway for around 15 miles or so, while smoke comes from under the hood when I park, but the car is not overheating. Also, it does this only if I was running the air conditioning in a higher setting when driving; it doesn't happen if the air was either off or on a lower setting.

Some additional points: (1) the coolant level is on the "min level" line exactly; (2) the air filter is pretty close to needing to be changed (and may need to be changed now anyways); (3) the engine does spew some oil (using the term loosely), but its no worse than i've seen with other '07 A4 2.0s; (4) i've checked the coolant line and wasn't able to find any obvious leaks; and (5) no lights/indicators are on currently.

I really appreciate any and all responses, and I'd like to thank you for your help in advance.

Any suggestions?