So I had this cheap Johnson 15W amp and was jamming with my brother...he played drums and I played guitar. Anyway, in order to hear me, I had to turn my amp all the way up and we played for an hour or two.

Now, when I play a low G...or like the 2-5 frets on the low E string, my amp makes kind of a low rattling noise at any volume, but is okay at higher pitches. Did I blow out my speaker?

I have another amp, so it's not a big deal...but I would like to have stereo sound (my effects pedal supports stereo output). Would it be possible to just replace the speaker? And is that easy to do?
checked for tears and didn't see any. so, i just tightened all the screws and at least for now, it sounds just fine. is this good? or do you think this is just a temporary fix?