A 1992 Buick LeSabre 3.8l engine has a rattling sound that gets louder when the A/C is engaged. Sam uses a long screwdriver on the compressor to feel it and hear the rattling sound. Guillermo removes the belt, is able to wiggle the slightly loose compressor pulley, and runs the engine. The total lack of noise at this point convinces Sam and me to go ahead and find a compressor from the boneyard. I wiggle the pulley on the replacement compressor - also slightly loose. I think, "If it rattles, I'll just send it back."

Guillermo changes it out but wants to run the engine with the serpentine belt on before mounting the refrigerant pipes.

 "It rattles, boss" said Guillermo. He takes it off, puts the other compressor back on, and we send it back. Good thing he didn't mount the refrigerant pipes.

 Back to square one. I decide this time to listen to the alternator, the steering pump, the water pump, and the idler pulley through a 3-foot length of heater hose for a stethoscope. Sure 'nuf I hear it the loudest at the idler pulley. I take the belt off and find a slightly wobbly idler pulley. I put the idler pulley around my finger and spin it. It feels and sounds worn out. I replace the $22 part. Same noise!

While I'm gone to the parts store, Sam inspects the other components and finds excessive end play in the steering pump as well as looseness in the water pump. He spins the alternator with the cordless drill and finds it to be quiet and smooth. He goes and brings back new replacement pump units. He replaces the steering pump. The engine still rattles. He replaces the water pump.

The rattling noise won't go away! This car's killing me, man!

 Now we have two parts replacers scratching their heads cussing and discussing what to ass-u-me next.

 "I'm not replacing that alternator!" said Sam. "You didn't even find the noise anywhere up there with your rubber hose!"

 Guessing wrong and chewing up the customer's meager funds is one thing but eating a $200 alternator is quite another!

 While Guillermo is doing a post-installation under-car inspection for leaks at the pump fittings, he notices the harmonic balancer has lost large chunks of rubber. He grabs it. He yells, "Boss! I found another loose pulley!"

 What did we learn? Beware of the guy who has the solution before he understands the problem.

 Product knowledge: Unlike the Mitsubishi crankshaft pulley which completely falls apart and loses the drive belts, this LeSabre pulley has interlocking 3-pronged failsafe that, in this case, failed to make noise until its pulley was driving the accessories. This would explain why parts closest to the crankshaft were condemned by Sam and me. The problem ended up solved by an enthusiastic trainee named Guillermo.

-Tim Campbell