one common cause of chronic hip joint popping is "snapping hip syndrome"
http://en.wikipedia.org/wiki/Snapping_hip_syndrome
the thing is, the audible popping can be from structures around the joint or inside it: meaning it can be as relatively benign as the ITB "snapping" over the greater trochanter of the femur, or it can b indicative of a labral tear within the hip capsule;
bear in mind that the hip joint itself is designed primarily for stability, and it's very difficult therefore to dislocate a hip joint: therefore, excessive hypermobility is not really such a great thing within the joint itself, as it's contrary to the main roll of the joint (stability in weight bearing); of course, it's fine to have good flexibility of the muscles around it, but that's different;
in my personal / professional estimation as a PT, any chronic popping in the hip (or any joint for that matter), is always an issue of some concern: as it suggests either dysfunction within the joint or imbalance of the structures around it, causing abnormal myokinematics, it stands to reason that over time, this can lead to further degeneration and then symptoms of varying types;
also, remember that when u attempt splits, or any sort of movement that requires "stretching", it's more likely that the structures that are prone to hypermobiity are the ones that are going to get further lengthened, unless u r very specific at targeting the hypomobile structures, but this is very difficult (Iyengar yoga approach does a great job at this sort of relative isolation); anyway, what ends up happening at times is the stuff that doesn't move stil doesn't move, whereas the stuff around it that was already prone to excessive movement now moves even more; of course, I haven't examined u so I don't know ur specific situation, but the one thing I'd look at is where in the lumbar spine / pelvis / hips u move from a lot and where u don't move from at all; that should give some idea of what's informing the grinding / popping, which, again, suggests some dysfunction in the area;
my suggestion would b finding a PT (or other similar discipline) that looks at things in a similar way to what I've described above; or u may try to find a certified yoga instructor (I'd go with Iyengar, hands down, any day); whatever u do, I suggest u do it before pushing urself further into ur splits, as u may b doing more harm than good (or not - u may b perfectly fine, I have no idea); if u r doing something innappropriate, better to ease off bef u do more severe damage - if after getting assessed there is nothing to worry about, any loos u may temporarilly experience will b nothing compared to the time u would b on the bench if u do injure urself;
good luck