I also had a loose spark plug. Took a while to track it down. Had the car a year now and chirp started a few months ago. I replaced the power steering pump (really not fun) and upper idler roller to no avail. That was before I read on the forum a tip to remove the serpentine belt and run the engine briefly.The chirp was still present meaning none of the things turned by the belt were causing the sound. (alternator, PS pump, AC, water pump, rollers, tensioner). Many on the forums indict the AOS (air-oil separator) but in my case, the AOS was on the opposite side of the engine from the noise, and there is no gray smoke coming from the exhaust; engine runs clean and smooth. Decided to change the plugs and sure enough, one plug was loose enough to turn by hand. Replaced plugs, torquing to 22 ft-lbs and noise finally eliminated. I would never have thought that spark plugs would loosen over time. Thanks all on this thread for pointing me in the right direction.
