Today I noticed that my wrx is idling weirdly. It's making a sound reminiscent of a diesel at idle when fully warm, which it hasn't done before...very rough sounding. I am 100% stock, maybe 19000 miles. I haven't checked anything yet, and I didn't get a chance to run it up to see how the performance is (traffic...). I had an oil change at the dealership about 500 miles ago, fwiw. Anyone else had this issue or know what may be going on?