When my a/c compressor is cycling on, it's making a clicking or thumping sound that is louder than before -- at least while driving at higher speed on an open road. It also creates a vibration I can feel with my foot on the floorboard and I think the engine is hesitating slightly more than I've noticed before. At slower speeds or while idling, there doesn't seem to be anything abnormal. I've never heard it switch on this loudly, nor felt the vibration with my foot like this. Since it doesn't mis-behave while idling, I've not been able to see what's happening under the hood. Thankfully the air is still good and cold. Any ideas what's going on? Thank you all very much!