A real puzzler.
Have you tried a startup using the DVD installer for that iMac to determine if it makes the same "sound" at startup running the DVD driver ?
In my way reasoning, the above "test" would show me that this sound may be coming from the DVD drive/mechanizim and not the internal hard drive mechanizim.
If you suspect that it;s " the Pro Speakers initializing, because it almost sounds like the computer is sending some kind of short-burst low-volume buzz through one or both of the speaker" have you tried muting down to zero those speakers ?
Are these the internal speakers ? You can actually kill the startup chord and those speakers if you are running your sound play back thru USB or a mixing board. If you need to know how let me know.
Have you tried a startup using the DVD installer for that iMac to determine if it makes the same "sound" at startup running the DVD driver ?
In my way reasoning, the above "test" would show me that this sound may be coming from the DVD drive/mechanizim and not the internal hard drive mechanizim.
If you suspect that it;s " the Pro Speakers initializing, because it almost sounds like the computer is sending some kind of short-burst low-volume buzz through one or both of the speaker" have you tried muting down to zero those speakers ?
Are these the internal speakers ? You can actually kill the startup chord and those speakers if you are running your sound play back thru USB or a mixing board. If you need to know how let me know.