Whine could have been a result of a lower than normal SC fluid level so that could explain why it disappeared.

The only time a SC should whine is under load (ie when your hammer is down on it) if its just at idle it shouldn't be that noticeable at all.

The other possibility is also an old SC belt - if they replaced that a new belt might have lessened the noise as well.

Bottom line - as long as your happy it's cool.