2002 Ford Escort squealing sound

Caradiodoc, It turned out not to be either one of your guesses. After doing a lot more internet research, I went into the direction of maybe the PCV valve or the crankcase breather element. So last weekend I took it to a large chain fast-lube place and they said my car didn't have either one but did pull off and looked at and put back a cylindrical part off an air intake hose which nobody I checked with still knows what it is called but is about 2.5" diam. x 1 inch high (just estimate but I am attaching a pic) To my surprise, for the VERY first time in over six months it stopped making the noise. And it stayed that way almost the whole day even though I made a lot of trips that day!! But then it went back to the usual squealing that evening. So today I went to a large auto repair chain and told them what happened so they pulled it off again and it helped for about two minutes so I knew we were on to something. So they took it off again and blew it out this time. They also said that they heard pressure being released when they started unscrewing the oil filter. And the problem disappeared again and is still working great after multiple trips throughout the day! I am so happy to be making progress. I am anxious to see if the sound is still gone tomorrow. Again, the sound has been constant for over six months. The only time it has disappeared is the two times that thing has been taken off and put back. Also I neglected to mention two things in my initial request for help that would probably have helped your diagnosis. The sound didn't start until I had driven the car about a minute. Also the sound stayed for about two seconds after the engine was shut off and sounded like pressure being released when it stopped

. So my question is, why do neither one of those big chains know what this little device is? I also realize that the little round thing might not be the thing that is being clogged. It could be anywhere down the line. What do you think the problem is?