I had the S166 in a usb case and the T166 lying on the floor(since the usb transfer was to slow for the initial data transfer of more than 100GB), so i did not compare them equally.
I did notice they were better than P120's. While i do think the S166 is quiter, that could be due to AAM settings, which i haven't double checked with a bootcd, i can set them while running(i have reasons for believing i can), just not reading them.
During initial transfer i did notice that the seek noise was a bit louder, however i have not heard such sounds again after building it in s(and setting AAM), nor have i heard them from the S166.
I won't be taking out the drives anytime soon.
The T166 just means it has 2 or more platters, the S166 is just a single platter drive.
Seek sounds are a little bit different(both much better than the P120), but i'm going to check aam to be sure that's not the difference (EDIT: aam was on for all drives).
EDIT: Once i'm sure the seek sounds are actually different, i'll try to explain it
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