I've used a synthetic caliper grease on mine. Has high washout resistance and rubber/plastic safe. Lubed the hell out of them when I installed them (I have both front and rear Si bars), and no noise at all. You can pick it up at any auto parts store. It's also great on your caliper slides, etc when you do your brakes.
So thats the noise I have been hearing? I want to get it fixed by Honda but I can't recreate the sound whenever I want. It just comes and goes and it is so annoying. This is the stock bushing squeeking? Mine does it out of the front right side of the car.