For sure get the MRI. I had something similar happen in early December. I went to the doc and he did a quick check, did a short ultrasound and said torn meniscus. He started to schedule me for surgery etc. I asked if he was positive and he said "yes", but if I "really" wanted to (he said this like an asshole) I could get an MRI. I got the MRI and it showed that my meniscus was fine. I had what is know as a partial dislocation. It pops loud, it swells a little and it hurts for a few months (around 6 months), but it doesn't require surgery, just some PT and afterwards a special brace that helps hold the kneecap in place.
I've been told by more than one doctor that lots of orthopedics push for meniscus surgery when it isn't needed. So take the time to get the MRI, find out who a really good knee guy in your area is (look for sports jerseys on the wall...seriously, my guy here had bundesliga soccer jerseys from all over Germany on the wall). Because if you get a guy that treats, sorry for this, older people or non-sports people mostly he/she isn't going to take into account that you are active and will push surgeries and long recoveries. Where a sports guy will work with you on not only healing and healing correctly, but also ways to help get you active faster again and will get you in touch with a PT person that works with sport injuries.
Good luck man and hope it is something small and heals quickly.