hopefully someone can help with this. as you know, the 08 CTS has two vertical rows of LEDs that are used for the each of the rear turn signals. anyway, for some reason only one of the LED rows in my left tail lamps is now working when the turn signal is applied. in addition, the turn signal sound is now twice as fast and the left front and rear (the only LED row still lit) blink twice as fast as well--as if there were a short or something. i checked the fuse and it's intact. any ideas??? thanks

Sounds like a connector is bad. LEDs don't burnout this quick and besides, they are not wired inseries so they won't al;l goout at once unless the connector is bad/loose.
Removing a part of the load will cause a an old fashioned TS to blink fast...that is the warning that you have TS problems. It appears that the simulated flasher in the CTS emulates this also.

Time for a trip to the dealership.