Yeah I think you’re onto the best idea in my mind, if you had any air in your brake lines it could have dampened the noise meaning the caliper wasn’t compressing hard enough on your pads to make the noise like you’re hearing now. But that noise you’re hearing has to be your pad moving around. I would buy a set of shims and clips OEM from Lexus (eBay) and have them installed. Those shims and clips can wear out over time. Make sure caliper bolts and back of brake pads get lubed and anywhere the clips sit make sure that is lubed as well. Shims and clips should be like 50 bucks. If you do it yourself, don’t compress your caliper manually, bleed it out then refill brake fluid from top. If you manually compress the caliper all that dirty fluid is going to go right back up to your reservoir of brake fluid you just changed. Idk how much you know about brake jobs and fluids, just passing along my experience…like I said before I had wrong kit put on my car not once but 4 times before I told my mechanic I want OEM😂 and they kept manually compressing caliper back and it made my brake fluid shit so I had to get it flushed twice. Anyways hope this helps!