I have the Invidia turbo back exhaust in an '08 hatch back. Loved the sound of the exhaust during the summer with windows down. Never noticed exhaust drone too much, or it just didn't bother me. When the weather got cooler in October, I enjoyed what seemed like additional power gains as my spirited pulls seemed a little bit more spirited. All was lovely. (cold air does increase power right?)
But, then I went on a road trip to Pittsburgh in November and hit temps of 40 degrees and even lower. The sound of the exhaust was no longer lovely as my ear drums were about to burst heading up into the mountains in PA. I chopped it up to high altitude and long distance driving at first. However, since December, I've had a ton of exhaust drone; its like a completely different exhaust sound--pitch and tone. I actually roll the windows down in the cold just to eliminate the subwoofer like boom in the cabin.
There must be something with cold-air, humidity, air density or something to explain this. Either that or I'm just trippin and getting progressively more annoyed with my exhaust, and I'm too old to be all race car-ish. Doesn't sound travel more efficiently in the cold? Maybe the air refracts when it hits the warm cabin from the cold outside, changing the note of the exhaust and causing it to have a flatter tone, more drone, and more cabin vibration.