My DD 6 months has picked up a new habit of wailing/singing/moaning just as she goes off to sleep. (Difficult to explain!) She doesn't sound distressed, just a little drunk 
She does this is she falls asleep in my arms, the car, pram, sling even sometimes feeding.
My question is, when she wakes in the night she sometimes makes this noise and goes back off to sleep on her own. But sometimes it progresses to more of a grizzle and then a cry. I have been going in to her as soon as she starts grizzling but am I disrupting her learning how to self settle? I am not interested in letting her cry it out, or cry at all for that matter. But don't know where to draw the line? What does everyone else do?