Thanks, yes male. You could be right about the "mud". I initially went to the GP to get something to relieve the pain and she thought it was likely a kidney stone and we'd give it a few days to resolve itself which it did. I'd sure like to catch that stone though to find out it's composition.
I think I read somewhere that a stone can literally bounce around in the bladder for weeks before being expelled.
i'm guessing by the "rob" that you are male. and my understanding is that males can feel the stone coming down the urethra after it comes out of the bladder. but i could be wrong.
i would guess that the rusty mud is probably old blood that your body is flushing out.
but my suggestion would be to call your primary care physician and tell them about it. they should be able to give you an idea of what it is and what to expect.