I also have a vibration on my 2008 Aspen. Bought new in November of '08 and it has had it since new (2400 kms on it now). Rebalanced tires twice, replaced all 4 new tires, replaced axels and still same problem. Taking back to dealer with some of the great suggestions. I dont think its a Good Year tire problem as I replaced them with high end Dunlops.
Update: March 9th. Just got Aspen out of shop with a new drive shaft, much better but still ocurrs??? Anyone got to the bottom of this?