Firmware version could have an effect, but doesn't by itself explain why my ST3120026A would be slightly faster, but still quieter.
Single-platter Barracuda IVs indeed have quiet seeks; the dual-platter versions, not so much (at least in my limited experience).
For what it's worth, here are the access times and subjective seek noise levels of some of my drives:
ST320011A 3.10 (AAM on): 14.2ms; silent
ST360021A 3.19 (AAM on): 15.5ms; moderate
ST310014ACE 3.09 (IIRC, AAM had no effect): 19.4ms; silent
ST340014A 3.04: 15.2ms; silent
ST340014A 3.06: 14.9ms; silent
ST340014A 8.01: 15.2ms; silent
ST380011A 8.01: 14.9ms; moderate
ST380013AS 3.18: 13.1ms; loud
ST3120026A 3.06: 14.7ms; quiet
WD800JD-00LSA0 (AAM off): 14.8ms; silent
ST31000528AS CC38: 13.7ms; loud
Access time and seek noise are clearly only vaguely correlated.
EDIT: My ST31000528AS reports itself as being AAM capable, but it has no effect.
Single-platter Barracuda IVs indeed have quiet seeks; the dual-platter versions, not so much (at least in my limited experience).
For what it's worth, here are the access times and subjective seek noise levels of some of my drives:
ST320011A 3.10 (AAM on): 14.2ms; silent
ST360021A 3.19 (AAM on): 15.5ms; moderate
ST310014ACE 3.09 (IIRC, AAM had no effect): 19.4ms; silent
ST340014A 3.04: 15.2ms; silent
ST340014A 3.06: 14.9ms; silent
ST340014A 8.01: 15.2ms; silent
ST380011A 8.01: 14.9ms; moderate
ST380013AS 3.18: 13.1ms; loud
ST3120026A 3.06: 14.7ms; quiet
WD800JD-00LSA0 (AAM off): 14.8ms; silent
ST31000528AS CC38: 13.7ms; loud
Access time and seek noise are clearly only vaguely correlated.
EDIT: My ST31000528AS reports itself as being AAM capable, but it has no effect.