The serpentine system has its good points and bad points just like a seperate belt system.. What I find about the idler pulley is it can make two different sounds.. one being a bad bearing.. When it starts to make that noise its only going to get worse till it breaks... The second anoying noise is from the spring inside the system..I'm guessing from when the pulley moves up and down the spring rubbing on the body of the aluminum casting makes a scraching noise....I'm thinking a bad belt is the main reason for this problem.. I have replaced these idlers with aftermarket ones , but they are not the quality of original...I have taken the originals apart cleaned and greased the inside and put on a new bearing...