I have a noise coming from the front (right side) (accessories) of my engine. It's a rattle that only happens at idle; it fades out and disappears when I accelerate and is completely absent at cruising speeds.

I've replaced the alternator, the compressor, and the serpentine belt in the last four months.

Does anyone have any ideas?

 

Have you tried to run it with the belt off? As you found out troubleshooting by replacing parts is expensive. Have you checked the exhaust manifolds and engine mounts. An exhaust leak can come and go and a squishy mount can allow the engine to drop and contact things normally out of reach.

 

Check it at idle with belt off as (other) eric says. While belt is off check for play in tensioner and all pulleys.

 

I have a similar noise in my Intrigue. It appears to be the idler pulley in my case, which I ordered last week from GM. They have bearings that dry up. Also, it could be the belt tensioner. The noise is only heard at idle and sometimes it completely goes away.

 

I haven't been "troubleshooting by replacing parts." I replaced the alternator because the alternator died. I replaced the compressor because the compressor clutch died.

I wouldn't know how to "check the exhaust manifolds," and the noise is not coming from the engine mounts.

 

When I replace a serpentine belt on a vehicle I usually just buy the Dayco kit that comes with tensioner and idler pulleys. It has been my experience that if I replaced the belt the idler or tensioner would need replaced before the next belt.