Not to downplay what is going on with your DS, I thought you had posted a cool video...

A friend was told the same thing about her DD and nothing became of it.

it could by congential hip dysplasia which can be corrected by the infant wearing a sling-mechanism to hold the hip in place.
when baby is laying on it's back (supine) flex the knees holding your thumbs on the inner mid-thighs and your fingers outside on the hips, then bring togther (to touch at the knees) and then apart (Gently!)
this normally feels smooth and has no sound.
If you do hear a click, it could be nothing... but it could be a dislocated hip which means the head of the femur is not cupped into the acetabulum but is resting posterior (ball not in socket)
it feels like a clunk because the head of the femur pops into place (this is a positive Ortolani's sign)
A hip click isn't the best way to test for hip dysplasia.
Look at the baby's thighs... are they the same length?
more importantly do the thighs have the same amount of skin folds along the inner thigh? Normally they are equal on both sides, and some asymmetry can occur, but if there is a great difference go to another pediatrician or experienced midwife.

**Breathe**

Probably nothing, but baby's ligament's growing and stretching, releasing gasses, etc. You could do some massage on it with the intention of opening the hip joint...you're in ny? I can recommend someone great for you if it comes to that, but honestly I wouldn't be worried.