For your case, I'd suggest that tyres are the issue, specially when they are widely known for being awful (Don't ask me how awful they are, because I never put them on, I've just read as you guys have)I'm from Toronto as well! I have a '15 GT and noticed two similar problems: 1) a vibration from around 40 to 50km/h, shakes the whole car a bit, and 2) a minor vibration at highway speeds that I don't feel much but know it's there since either items in the car or the steering wheel you can tell are vibrating.
So far the first issue at 40ish km/h, I've tried fixing with an alignment and balancing. Worked for like the first few days, but then I noticed the vibration coming back. They said they put some weights on the rim to balance it too, but I don't know, was like a temporary fix. Then I got aftermarket rims and noticed the problem disappeared for a few days too, but came back... So far my suspicions are with the OEM Dunlops which have I've been using all along. Don't really feel like dishing out for new tires at the moment as they're relatively new. Hopefully someone else has an answer to this.
Thanks for the suggestion, I'll look into force balancing. I suppose it could also be that I'm just not used to 19" wheels, the largest wheels I've had prior to this were 17" on my 09 Accord Coupe. The 19" on the 6 are just so gorgeous though. :crying:Force balance it and see if it shows any improvement. Vibrations are notoriously hard to identify, it can be anything from a rim which is bent, a tire that has minute deformations, suspension or steering parts or something else. The 19 inch rims as good as they look, do take a battering on bridge joints and potholes. The only car i ever owned with the smoothest ride and little to no vibrations even after thousands of miles was my 97 Camry with 14 inch steel rims ! Larger the rim size, more the headache with balancing and vibrations.