After upgrading to yosemite my macbook pro late 2011 does a random sound from time to time.

In SystemPreferences->Notifications set "Do Not Disturb". Restart. Any change?

If not, can you describe the "sound" a bit better?

is it like a clicking sound? If yes, restart while holding the CMD+R keys, from the menu choose DiskUtility, it starts in the FirstAid tab: choose your start up disk, do "repair disk". See what the result is. Your disk may be dying.

Sounds like Notifications app.

Maybe some other app. In SystemPreferences->Users&Groups->LoginItems tab: remove all entries with the minus sign underneath. This will not uninstall anything, you have to start those apps by hand now. Restart.

Still there?

Yes: Restart again while holding the shift key, this will start the mac in SafeMode: only the necessary items are loaded to run.

Still there?

Yes: Make an etrecheck list and post it here.

No: Restart, put the items in the LoginItems back, one by one, restart after each entry, and you will find the "culprit"

Please report accordingly. I will be back in 24 hours.

PS: of course you do this with all external equipment disconnected.

Lex

"i switched off the itunes helper on login items..."

You do not need that at all in the Login Items, so you do not have to bring it back: it comes up when you need it while using iTunes.

Good that it is gone away. did you do the start in SafeMode? That is a good way to "reset" the machine.

Lex