I have been testing and “burning in” two identical drives for storing many years of photography work (large photoshop/photography files).

Both drives have tested fine in multiple tests (e.g. short and long smart tests, surface tests, etc.).

I am currently running a butterfly test on both drives and have noticed that one drive is so quiet it cannot be heard over the quiet fans on the workstation while the other drive is very noticeable and sometimes can be heard across the room.

For the nosier drive, the sounds are similar to seek sounds on noisier drives from 10 years ago. The are soft movement sounds and not hard clicks, scrapes, scratching, etc. So, I don't think what I hear indicates imminent failure. In fact, if the quiet drive was about the same sound level as the noisy drive, I'd probably accept them as noisier than average drives and move one. However, since one is nearly inaudible and the other relatively loud, I'm wondering whether the noisy one is not "up to spec" and may fail faster.

Another data point, the noisy drive temperature runs 44-46C while the quiet drive runs 39-41C.

I’d appreciate advice on this!

Different AAM settings?

https://en.wikipedia.org/wiki/Automatic_acoustic_management

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A backup a day keeps DR away.

Great idea! I checked with HDTune and it shows that neither drive has AAM enabled.

What are the full model numbers of each drive? Date of manufacture?

Sometimes a drive may have more platters than another, but with some heads switched off.

WD models may have the same base model number but different suffixes. The suffixes identify the family.

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A backup a day keeps DR away.

They really are identical drives. Seagate Ironwolf Pro 3LY101-500 with the same firmware ENO1. Both Feb 20, 2023. Brand new, direct from Seagate themselves.

The drives are both at 81% of a complete butterfly test on the entire drive with no concerning results. It does seem like drive noise is a bit lower overall; however, it is not quite right now (roofers working on the place next door).

Temps still about the same.

Are the first 3 digits of the serial number the same?

Yes. Both are "WPO."