Hi guys, My engine (123K miles) has had a small whine over the last few months, nothing too bad but definitely noticeable. It was more prevalent during cold winter days. Last week I was driving it and the noise started to get a lot worse to the point where I heard a metal on metal scraping noise. I immediately pulled over and checked the engine. I narrowed it down to a bad pulley. I drove it back home and it has been in the garage since. Once home, I released tension on the belt using a ratchet on the belt tensioner and spun all the pulleys. The two pulleys that make noise are the two circled in red on the attached image. The bottom one is really loose and make a lot of noise when spun while the one on the top is noisy but nothing like the lower one. Are these both referred to as the idler pulleys? I did some research and came up with Motorcraft Part #'s YS249 (lower ribbed pulley) and YS245 (smooth upper pulley). Should they be replaced with Motorcraft or is there a better brand out there? Lastly, is this an easy repair? The smooth upper idler pulley looks very easy to replace. The ribbed lower pulley looks more difficult (it has a AC line dryer in front of it) and I have researched this problem and have seen people mention that this one is reverse threaded. What exactly does that mean? I am not super technical but I have done some repairs to the car. Does this require a mechanic or is this something pretty easy to get done? Thanks in advance for your help! P.S. attached image isn't my car, just found it on the web and put circles on the problem areas.