iMac 27" 2020 -FAN IS NOISY

You still didn't answer the question. What RAM did you purchase from Amazon? OWC? Crucial? Kingston? Hynix? Micron?

Read through this thread... one major issue that I had with my (then new) 2020 iMac was constant crashing, and the fans running very loud.

https://discussions.apple.com/thread/251962728?answerId=254170742022

The problem turned out to be OWC RAM. All diagnostics showed zero problem, but the RAM - regardless of OWC's stance - was found to be faulty. The RAM was causing my CPU to run much hotter than normal, resulting in the fans kicking on while doing the most basic of tasks. All problems immediately improved the moment I removed OWC and installed Apple OEM RAM from Micron (Via Crucial). The CPU/GPU temperatures went down almost 20(F) degrees after switching RAM.

I bought my RAM through Amazon, but by the official Crucial store on Amazon so I know I was not getting any sketchy RAM.

Before throwing money at the problem, did your iMac behave this way since you upgraded the RAM, or is it a suddenly new problem that began? If it's been that way, an option you can try is for you to re-install the OEM RAM your iMac came with, and remove all 3rd-party RAM. Does the FAN noise disappear?

Many people with 2020 iMacs have had problems with OWC RAM. Apple and OWC have remained quiet on this.

As you have until July 3rd, another option would be to buy Micron RAM (by Crucial) and try it out. You still have a couple weeks to return that one as well.

It took me three months of constant problems with my 2020 iMac, along with multiple RAM swaps by OWC until I figured out the problem. Thankfully, the 3rd-party reseller I bought my iMac from also installed OWC RAM at purchase and three months later still refunded me the full amount for the RAM where OWC would not do it.

Re-install your original Apple RAM. If the fan noise goes away, that says something.

Re-install your OEM memory and see if the problem persists. I don't trust OWC RAM for the 2020 iMacs, but you should do some basic RAM troubleshooting as well.

That could be your issue. Please, for testing, remove the OWC RAM, and reinstall the Apple RAM.

-Jack

Please Use Apple Diagnostics to test your Mac - Apple Support and let us know the reference code.

-Jack

As an owner of a 27" 2020 iMac, your concern brings up a lot of similar issues when I bought mine. So to determine if your issues could be the same thing, you mentioned your iMac has 64GB (mine has 128GB). Did you purchase your iMac from Apple configured with 64GB of RAM, or did you install it yourself?

If you installed it yourself, what brand of RAM did install? What is your RAM card configuration? 4x16? 2x32?

If it's from Amazon, it probably isn't compatible. What brand and model it is, specifically?

-Jack