On occasion, I find my 06 Sonata LX unable to lock the doors manually (by using the rocker switch on the driver's door). I have tried doing this while the car is driving (high and low speeds), parked, and not running. It doesn't always do this, it is rather intermittent. I am afraid if I bring it to the dealer, I will get no where because they can't troubleshoot it or duplicate this. Any help?