2008 R350 Both idler pulleys and tensioner are new. So is the water pump. Squeal, like loud cricket chirping, appears to be coming from upper idler but when I install old one it sounds the same. Squeal is most pronounced when engine is cold. Could this be the new aftermarket water pump? I tried using metal bar as statoscope on bolt heads of two idler pulleys but heard nothing like the squeal on them. I can’t do that to rotating hubs like water pump, alternator, ac & steering pumps but the noise appears to be coming from opposite side of drive belt at upper idler.
