Hi, Blizna ... I have experienced tendon "snapping" in my hip joints (I think of it more as a thumping.) I had this about 8 or 9 years ago ... it was very annoying, and loud! I could feel the hip joint go thump, thump, thump as I moved my legs. Even turning over in bed produced it. And in Pilates class, the whole class could hear it and teased me about it.
I asked my doctor, and he said it is simply the tendons drying out ... probably from age in my case, but perhaps overuse and physical stress (i.e., wrong exercises that strain the joint) contributes to it too. What happens is that the synovial fluid that cushions the tendons in joints begins drying out, and so the tendons themselves dry out and can't move smoothly. They move in a jerk-jerk-jerk pattern.
Anyway ... there are things to do about it. One is joint replacement. Another is a fairly new techique I've heard about in which surgeons inject fluids back around the joint. The third has worked perfectly for me! It is doing an exercise in Pilates that specifically targets the hip joints, and little by little over the past five years, that jerking of the tendons has gone away completely. Even though i'm getting older every minute.
I continue to do this exercise with the "normal" springs the exercise calls for. (I've cut back the resistance I use on other excersises, because of ALS.) But apparently, you can restore the fluid around your joints with safe, careful exercise.
Anyway ... hope this helps. The snapping (or thumping!) has nothing to do with ALS.
(By the way ... you won't get this exercise in "East Coast Pilates," only in "West Coast," which is more creative and free, and more related to dance. )