Fenders... and why I'm an idiot

[Tri Girl]

So I've never had fenders before on any of my bikes. I got a touring bike (old- from a pawn shop) and I've been riding it to work. We've had lots of snow and the result is lots of sand on the streets once it's all gone away.
I was riding to work last week (when it finally dried up) and kept hearing this noise that sounded like my fenders were rubbing my tire. I stopped, checked for clearance (there was plenty) and kept on. The noise continued. I was getting irritated.
Then, after an embarrassingly long amount of time- I finally realized that the noise was all the sand hitting the underside of the fenders. DUH!!! What an idiot. I've never had fenders so I didn't think about all the sand/road debris that was hitting the underside of the fenders. They're plastic, so I don't know if metal is just as loud with all the debris- but I feel so dumb for not immediately figuring that out.
What a dork I am!