car: '06 Hyundai Sonata, 3.3L V6 engine (chain-driven), 85K miles, always properly tuned
Warmer outside air temp (above 70ºF)...
* engine runs quieter, with less vibration
Cooler outside air temp (below 70ºF)...
* engine runs louder, with more vibration, even after a driving for more than 30...