What sound do llamas make?

I am on one of my fitness kicks and this involves 6,000 steps a day, not the obligatory 10,000 since a fitness trainer once told me there is no evidence for 10,000, that it is a number plucked out of the air and all you need to increase aerobic fitness is 6,000 steps a day.
 
Oh yes, and I use the free  Active Ten NHS fitness app ,which states you only need a minimum of ten minutes of aerobic walking a day to achieve a minimum level of fitness. Well, all that sounds very doable.
 
I mention all this because I seem to be blipping lots of scenes from my daily walks like this one today with a view towards Dunblane and the Trossachs in the distance.
 
It happens to pass the field with the four llamas (see extra). I tried to coax them to come closer by playing them some YouTube videos of other llamas on my iPhone.  
 
They were startled at first but did not move an inch despite me playing a variety of llama sounds.
 
However, the surprise was the strange sounds llamas make, a kind of high pitched humming