Yup- I'd go with silent runner on that one.
Get an MRI if you can.

It may take a while to get one, but its better waiting x months for an MRI, and the results in order to find that its something that can be rehabbed, rather than going the whole hog, getting something taken out of your knee that can't be put back and stops you running as well as you could for the rest of your life.

I know a couple of people who have had meniscus tears in the past, and haven't gone for surgery- they are now running better than ever. (that being said, every situation, and every body is different) Get several opinions before committing to anything.