Thanks for the compliment. There certainly a lot of guys on here that really have some helpful knowledge and experience....and they all share the desire to help out by sharing it to those who need it.
I'm assuming when you said your compressor "packed it in" that means it died. It's hard to tell if the noise you are hearing is normal or not. It's just so hard to tell what it sounds like with written descriptions. Do you have the ability to make a video so we could hear it? Nothing against your description, but you can imagine how it would surely help to be able to hear it for ourselves.
Before I delve into details here....is there anything you can tell me about what this A/C system's history has been? Have you ever had a leak? Have you ever had to add refrigerant? Any details about the actual failure? Anything you can say could help.
Obviously, the new compressor and system is working fine and you are getting cold air...but you should be concerned about the noise since it might not be working for much longer. You do have one advantage here that some of us wouldn't have if we did it ourselves vs a shop. It sounds like they are treating you well and I'm sure there is some kind of warranty on the repair....right? How long is it?
Now, A/C compressors will make a slightly different noise when first installed and will go through a "break in" period, but in my experience....it usually is something that only a knowledgable person would even notice. I'm only talking about someone like myself that would be listening for stuff like that. The fact that you noticed it does raise an eyebrow and does make me a little bit concerned. Don't be quick to make a conclusion something is wrong yet. There is a lot of details that have to be answered on the repair that only the shop would be able to answer. Before I go through a crash course on repairing a failed compressor.....Are you sure that it is the compressor making the noise? Does it go away when the compressor shuts off? Has it lessened in intensity at all over the number of miles you mentioned?...gotten worse?....same? Did they replace your belt as well?
Compressors do come "pre-lubed" with PAG 150 oil. You can't just throw the new one on there and assume that it is the correct amount. The system oil isn't only in the compressor....it's found in every component. I always drain and measure the oil that comes out of the old compressor so I know what amount to use in the new one. Your total specs as far as capacity on that system is somewhere between 9-11 oz of oil total (entire system).
Here are the guidlines that GM recommends on a compressor change.
*All Compressors (drain and measure the oil)
- If less than 30 ml (1 fl oz) is drained-add 60 ml (2 fl oz) to the new compressor.
- If more than 30 ml (1 fl oz) is drained-add same amount that was drained to the new compressor.
What else did they replace? Just the compressor? Do you know if they flushed the system or not? Personally, I have always flushed an A/C system when replacing a compressor that failed. Reason is that unless you do this....you have no way of knowing how much oil is in your system. Doing a system flush is not only important for the reason I just mentioned (removing all oil so you know how much to add).....it also serves the purpose of getting any sort of contaminants or moisture out of the system. A catastrophic compressor failure could have introduced pieces of whatever that could clog up lines. You have to remember that you really don't know what caused the compressor to fail in the first place. It could have been caused by contaminants in the system, or because it didn't have enough oil in it to begin with, etc. Flushing is the only way to ensure that you are starting at square one. I know some shops skip this step and others always flush them regardless to be on the safe side. There are a lot of "unknowns" here that you need to provide if possible and it might take you asking the guy who actually did the repair. Don't freak out if they didn't flush it. Like you said....it is working....so you probably don't have any blockages in the lines. However....even they didn't take the precautionary measures of flushing....it is an absolute requirement to drain the oil and measure how much was in the old one....and do the same with the new one so you can at least match the two. The noise you are describing could be just a bad reman....or because it has the improper amount of oil in the system even though the new compressor was "pre-lubed". The ccompressor comes with about 4 ounces in there...but there is no guarantee and is why you should always at least check by draining it and measuring it. Does this all make sense? I have no idea if they did all this or not....but your compressor obviously isn't liking something here since you noticed it and could have easily been caused by a sloppy repair....or because it is just a bad reman.
Did they replace the accumulator/dryer? The accumulator/dryer should be replaced if the system is left open for any period of time over a few hours. Again, to be on the safe side....I usually replace it anytime there is a catastrophic failure of the compressor.
Here are some more excerpts from GM on the accumulator/drier....as well as the evaporator and condensor related to oil.
* Accumulator-Add 105 ml (3.5 fl oz) of new oil to the replacement accumulator to compensate for oil retained by original accumulator desiccant and bag assemblies. The accumulator should only be replaced if leaking due to a perforation, damaged O-ring seal seat, or damaged threads.
* Evaporator-Add 90 ml (3 fl oz) of new refrigerant oil.
* Condenser-Add 30 ml (1 fl oz) of new refrigerant oil.
I know this can be complicated and tough to understand at first. You were right to be concerned....but before you consider what you need to do next....you need to find out as much as you can so you can make sure that you make the right decision here and either leave it alone or take them up on their offer to basically do the repair again. Because there are a lot of factors here as far as what could be causing this that were directly a result of the repair....you don't want to have them do it again. I would be suprised if a lot of the things I mentioned that need to be done were overlooked or skipped by the shop....so don't make the mistake of assuming they did something wrong. You just don't know yet. If it were me, I would do your homework here and do your best to understand what I have mentioned so you know enough to ask them the right questions. If you don't, you won't find out what you need to know because they think it will be over your head. Make sense?
There are just WAY too many unknowns at this point for me (or anyone) to tell you with any certainty what the problem is....but you are smart to be concerned IMO. Especially since the shop seems to be so willing to do the repair again. They might be aware of something that the wish they had done differently and are worried that it will fail before the warranty runs out. I will be glad to continue to walk you through this and share what I know. I am not what I would consider an expert here...but I think I know enough to help you diagnose this and help you to understand what is involved here so the shop will tell you what you need to know. A little knowledge here will go a long way to you getting this right and having an A/C compressor that will work for as long as the first one did (assuming that it was original).
Hope this helps.