Knocking Sound

Not see much for odd noises from the 2.7, but you might look at your crank damper for seperation of outer ring (pulley) from center hub.

A/C compressor could make noise, does it change with clutch off or on ?

Have had chains on top of head that ties the cams toghter, but that is more of a hash type noise I think.

If engine neglected (missed oil changes here-there), might could start a rod/main knock, but that is something we dont see, had 1 drop a cylinder liner on #6, but the engine would not run there.

Just spend some time with ear probe (long skinny screwdriver work good), take the drive belt off to take alt - a/c - p/s out of the loop, see if it go away or still there, that;ll cut some of the background noise. Have heard of random drive plate cracking, see if it change tone when put in gear and load the throttle a little bit (light stall test).. try it in reverse and drive..

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I only hear it at idle..... even when the A/C is running... I'll try the taking off the belt...

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I read your initial post again, with the belt off, I want you to roll the pulley on the A/C compressor, verify it is smooth... it has a 2 row ball brg in the pulley to compressor nose... take and grab the pulley, and see if it has any unusual excessive slop/lash in the bearing, if so, then replace the pulley..

There is the plastic idler pulley by the compressor where the belt come down from P/S pulley to make the turn to the A/C pulley, those sometimes make noise, but not very often,, it has a single row ball brg in it.

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