I dont know anything about any maintance mode as i basicly know nothing about anything newer than os3.1. But do you notice any perfomance issues when this click happens? like maybe the drive(s) stop responding for a moment or something. It could be a hardware issue, like maybe power issues after you added a new device. I know if the platters are not spinning fast enough, something similar could occure.
I have had this happen on a ide disk before.
