Why sound volume re-sets itself to highest level on cold-start or re-start (Maverick)?

Try resetting your PRAM

follow this article - http://support.apple.com/kb/HT1379

ok, that's a standard hardware reset,

There's more we can try.....

Open finder

from the menu items on the menu bar choose

Go/Computer

now click Macintosh HD/Library/Preferences/Audio.

within that folder, you will find audio .plist files, either delete them or drag them to your desktop.

Now set the volume on the machine to your desired setting for startup.

Next restart the mac. These plist files will be automatically re-created by OSX when you restart and hopefully things will be back to normal.

The trash-the-.plist trick for corrupted .plist files does not work for Mavericks, as Mavericks caches preference files. This page from Topher How to tackle defaults not sticking in Mavericks - CNET has some suggestions that may help fix the problem.

Sound Levels - Troubleshoot

try setting your deired sound level, then start up in safe mode to eliminate any third party apps that may be interfering with your settings.

To start up in safe mode, turn on machine then immediately hold down the shift key until a progress bar appears under the apple logo on the grey loading screen. When this bar appears, you can release the shift key.

When you get to the logon screen you will see "safe boot" in red at the top right hand corner.

Log on using your usual account name and password.

test the sound level in this mode. Be aware that 3rd party apps will not function in this mode and graphically , things may be a little "jerky", this is normal.

If the sound behaves in safe mode then something you have installed (non Apple) is causing your issue and you will need to uninstall all 3rd party apps from your account and reintroduce them one by one until you find the culprit.

If safe mode presents you with the same problem, create a new user account on the mac (you can delete it again later).

Log in using the test user account and test the sound levels again (setting to low, restarting and logging back into that same account). If the problem persists in a test user account too, then I would suggest that you perform a Time machine backup up and try to reinstall OSX

Let us know how your testing goes......