Noise: AC Compressor or transmission

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zrxinch

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01 V8
Been searching for a while and this is the closest I have found to my problems.. http://www.lincolnvscadillac.com/forum/showthread.php?p=6590
Loud moaning sound that only happens at idle to 1000rpm when hot.
Just like in the above post yet here is the crazy part, when I turn on the AC I never hear the noise, when the AC is off it only does it for a short while after I get off the freeway after I come to a stop and hit the gas to start moving again. So I believe it is probably the compressor clutch.

Here is the crux, when the car is stopped only after it warms up AND only in park or neutral, I can ever so slightly hear a different grinding noise which I believe is coming from the tranny. Tranny was rebuilt 30k ago btw. Pretty sure the grinding is planetary gear related and not pump.

Where I am not sure is if the moaning noise I believe is from the AC compressor is actually the tranny pump starving for fluid due to level or filter issues. Haven't checked the level but plan on doing that tomorrow.

Wondering if anyone has any experience with either of these sounds lately?
 
Update, its not the transmission, fluid is full. The grinding is actually what I believe sounds like the beginning of the timing chain guides wearing out (108k). The moaning sick cow sound after I get off the freeway def sounds like it is coming from the compressor / alternator area but now that I have been aggressively trying to isolate it I realize it does it regardless if the ac is on or off. AC seems low on charge because I have the hissing sound and it struggles to blow cold when it is hotter than 80* outside. I wouldn't be surprised if the moaning was from the alternator but it doesn't make sense that it only does it after driving on the freeway and then it is only for a short while, it is actually hard to diagnose because it goes away so quickly after about 5 minutes. Very frustrating.... I am not going to just throw $$$ at this car and hope it goes away. Looking for any ideas or experience with this. I plan on pulling off the freeway after work today and getting a video of the sound.
 
Are you sure about the location of the "moaning" sound? Most of the time, when the sound is a moaning like sound, it is coming from the engine air intake and is often related to a slight problem with the IAC.

You would be wise to check the bottom of your AC compressor for signs that it is leaking compressor oil. If it's not, then adding some R-134a should be all you need to bring it back to correct operation.

The grinding noise might still be the AC compressor clutch. I've heard them make this noise when the AC is off. In your case, since the refrigerant is low, the clutch still may be cycling off while the AC is on.

Normally, when the timing chain tensioners are failing, the noise is a rattling sound from the front of the engine, most often heard at cold startup.
 
UPDATE:

Turned out to be the alternator. Sounds on these cars do travel to strange places.
 
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