Question My friend has two identical hdds but different trasfer speeds! !!

Mario Italia

Great
Jul 12, 2020
145
3
85
So my friend got twI identical HDDs last month, and when he decided to run benchmarks using HD tune he noitced the maximum transfer speed is like there's 10 megabytes per second difference btw the harddrives, also he noitced the non os hdd is slightly slower then the os one, by the way both hdds use different firmware revision.
WD Red Pro 4TB NAS Internal Hard Drive - 7200 RPM Class, SATA 6 Gb/s, CMR, 256 MB Cache, 3.5" - WD4003FFBX
 

Mario Italia

Great
Jul 12, 2020
145
3
85
A friend is running two identical HDDs in the same case, same specs and same model, but when he benchmarked them, he noticed there is like 10 megabytes per second difference in transfer speed, also one is louder and slightly faster and two hdds have different firmware version, is it normal?
 

Mario Italia

Great
Jul 12, 2020
145
3
85
How did he "benchmark" these?

Please show screencaps of CrystalDiskMark results.
He lives in different city and he used HD tune to benchmark them, the louder and the faster one scored 180mb/sec transfer speed and slower and quiter one scored 167mb/sec at peak, like I said they are identical model but different firmware revision.