popping post acl reconstruction

Hi, I had an ACL reconstruction about 6 weeks ago. Recently I’ve been experiencing a popping sensation in my knee towards the end of a long day. I tried to explain it to my physical therapist, but found it impossible to. What I told him was that it felt like when I bend my knee my kneecap gets stuck under the bend and then slides up over it after a hesitation and pressure. I later realized that I could make it do this if I first straightened and tightened my knee, however by this time I was no longer at PT, but at my team’s soccer practice (I wasn’t playing obviously) When this usually happens to my knee its not like I’m hyperextending it and thats causing it, it just happens. So I showed my friend because it wouldn’t do it for my PT so he didn’t know what it looked like. My friend cringed when she saw it and said there was a lump that started at the top of my knee and travelled even farther up and over the knee cap so that it travelled about 3 inches in total. I finally was able to show the athletic trainer at school when I went to see him when I experienced weakness, pain, and popping in my knee. He did feel the popping and said it was the patellar tracking that was causing the popping/problems but also that it’s not a big deal. I was wondering if you could tell me about this or if you’ve heard of this. I don’t understand why I would be having this problem. I was misdiagnosed with a medial subluxation due to a failed lachman’s test but that was thrown out when the MRI proved an ACL tear. I was wondering if I could have done both (subluxation and tear) and if the subluxation would have shown up on the MRI. Also do you know of anything I could do for this and if it is a serious or common problem post ACL reconstruction. Thank you for your time and help!