I'm going to throw something out that some may not agree with.
I recently read a book called 'The Aware baby' some of which really annoyed me, however the author made a point that I have never considered before. She said that children feel safest with their parents and if they are feeling stressed etc they sometimes just need to cry as it is the main way they have of expressing themselves and as an outlet for their emotions. In this instance we should not try and distract the child from crying as we are teaching them that we don't want to hear them. Also if we suppress this need too often (i.e. with too frequent comfort feeding or overuse of a dummy) the need to express emotion can come out in more physical ways such as hitting, biting etc.
They are more likely to do this at home with their parents who they trust (Hence well behaved children with child minders who tend to cry and fret when they are with their parents).
She suggests that if you are sure there is nothing physically wrong (not hungry, thirsty, tired, bored, ill etc) that it can be helpful to just sit with your child (and depending on their age reassure with touch, cuddles or words) and allow them to cry for as long as they want to but always with you there providing your full attention.
I have occasionally tried this with ds when he is being really whiny for no discernable reason. i.e., he is just fed, watered, milked, woken from a nap etc and is winging with no amount of distraction working. You have to be pretty certain he is not ill which can be difficult to know. However when he is having a whiny week I have on occasion taken him to the doctor to be sure he is not ill as he is crying so much. If he is OK I just let him cry (always with me there).
It is much less stressful for me as I just surrender to the fact that he wants to cry and after a while he stops and either falls asleep or finishes crying and gets on happily playing again. He sometimes does this a couple of days in a row and then I find he is better for a while and less clingy.
The author suggests that the child just needs to be heard and paid attention to despite being angry or whatever they are feeling.
I think there are some (admittedly limited occasions) where this works and I was amazed that although it is difficult to hear ds crying it is far easier than the days of whining that tend to precede it.
Just a thought
Anna