Hip flexor trouble - snapping hip syndrome?

[SS2016]

I got back into low bar squats after a long break due to injury on Monday and I've already fucked myself up. Every time I lie down on my back, flex my bring my left knee towards my chest, then lower my left knee, I hear an awful popping/snapping sound. The only thing I can assume that brought this on was going back to low bar squats and doing them incorrectly. I dont know if it was due to tight adductors, not shoving my knees out hard enough, shoving my knees out too hard etc. When I do a bodyweight squat, I feel a slight bit of pain in my left hip flexor, but nothing major. The popping doesnt happen when squatting, only when lying down and flexing and extending the hip, and when standing up and flexing and extending just my left hip.
After spending a few hours researching my symptoms, the only conditions that seem similar to mine is snapping hip syndrome or hip impingement.
Is there anything I can do in the meantime to try to fix it, before spending a shit load of money on a physio/doctor?
Thanks

[Mark Rippetoe]

You can learn to squat correctly. See today's video: Starting Strength

as well as pages 51-56 in the book.

[John Hanley]

I've got it. Had it my whole life. If I palpate the front of my hip during flexion/extension, I can feel tendon getting caught on the bony prominences.

Consider it a blessing: it's a feedback mechanism that will alert you to knee-slide in the squat. If it's inflamed, thunking & painful, you fucked up. A much more powerful reinforcer of sound mechanics than any tubow.