The answer to 'why is my gutter odor' is that a foul smell in your gutters is usually caused by the buildup of organic matter like leaves, twigs, and debris. As this material decomposes, it can create a strong, unpleasant odor. Gutters that are not regularly cleaned can become a breeding ground for bacteria, mold, and other microorganisms that contribute to the odor.
The symptoms of a gutter odor problem include a strong, musty smell coming from your gutters, which may be especially noticeable after rain or when the sun heats up the debris. You may also notice visible buildup of organic matter in the gutters.