This morning, pulling between two cars at the parking lot at work I noticed a new sound from under the hood. Not good. It sounds like something ticking but is irregular. Opening the hood, it sounds like something attached to the drivebelt, but that leaves plenty to choose from:
tandem pump, AC compressor( it was the same with AC on or off) ,
water pump, airpump, alternator and the belt tensioner.

My questions are does anyone have a method for diagnosing this kind of noise? (I like to keep my hands and ears far from the fan)

Which of list list of components is likely to fail first?

Anyone have a similar experience at around 143k miles?

Thanks to all,

__________________
Tim Benner

00 ML320 170K
95 E320 wgn 160K