Ask Max: Random Startup Chime Volume
With my present four G4s, perhaps my previous G3/300, and my G5/Intel/iMac, I have noticed that randomly, the Startup chord is of "normal" volume and other times the internal speaker is almost to the point of being overdriven. What controls the level of the volume of the Startup chord?
The startup chime is mostly controlled by the Mac computers system volume that was set prior to being shut down or restarted. Under normal circumstances the volume information is stored in the PRAM, and on next boot your Mac will load that information into the active settings and then play the sound. There are times that this is not the case. If your PRAM battery has a low charge, the volume will default to its highest settings. This is the same when you" Zap the PRAM" via holding down the [option] [command] [R] and [P] keys.
Also a software glitch or system crash can have unpredictable results on the startup volume. If you can't control the startup volume with the system volume controls, then check that your system has a good PRAM battery.