Grumbling vs complaining

A few posts ago, I spoke of how the writers of Scripture envisage Christians as people who do not grumble, so confident are they in God's goodness and sovereignty.

However, the Bible does positively hold up believers that complain... The Psalms, for instance, are full of incidents where the psalm writers open their hearts in complaint. So what is the difference between grumbling and complaining? How can I make sure that I'm a complainer and not a grumbler?

The difference to me seems to be the focal point of my problems. In Psalm 6, for instance, David complains about all manner of things in his circumstances (including his enemies, and illness in body and spirit). His response, however, is not to grumble but to complain: to place all of his concerns into the hands of the LORD, knowing that the LORD alone is one that can help in this situation. Even though his circumstances are the subject of his prayer, the complaint is God-centred (isn't this the thrust of Philippians 4:6-7).

It would seem to me that, whilst grumbling is always a danger, it is possible to complain in a godly matter in conversation with others too (particularly when the audience of complaint is also wary of letting the conversation drift into grumbling).

It would also appear to me that (despite the danger of grumbling), it is sometimes right to complain, particularly when, in some way, God does not appear to be getting the glory he deserves or, from what he has revealed about himself, his will is not being done. For example, whilst the danger is always that it will spill over into grumbling, it is right that injustice or church gospel disunity causes us to complain (primarily to God, but sometimes to each other).

Any other ideas on how we can complain in a godly way, but not grumble?