A friend has a '97 PSD with an automatic that has recently started to make an unusual noise. There is a kind of buzzing, card in a high-speed spoked wheel, sound under even the slightest acceleration. It changes pitch with RPM and at shifts, and, goes away as soon as you let off the throttle. He says it has gotten worse over the last 2 weeks.
Any ideas?

 

He got his answer today. Tensioner pulley for the serpetine belt flew off - missed the radiator.