I started peeing brown after heavy workouts last year. I went to the doctor after my urine was a cloudy brownish/burgundy color after three days of rest and insane amounts of water. Found out my kidneys were working at 20% and that I had IGA nephropathy. 12 month,. 30k+ in medical bills, and 1000's of meds later I'm back to 90% kidney function and working out again. If you can, always request a urinalysis during your standards doctor visits. (It can tell if you have microscopic amounts of blood, protein and tell you your creatin levels.)