I've been getting this intermittent noise at idle. It could be happening while driving too, and I just don't hear it. It sounds like a "wub wub wub wub wub" noise, and lasts for about 3-5 seconds. Seems to happen randomly. It kind of fades in and fades out. Makes me think of like a pump turning on then off. This happens with the AC either on or off, just sitting at a light or parked in a lot, not turning the wheel, pumping brakes or anything--just sitting still in the car. Any ideas where to start? Maybe a bad pulley? PS or water pump? Car runs good otherwise, no codes.