I went in water a little deeper than I should have a few times and because of that I've taken on some water before. Since the first time it's happened I had pretty much brown speaker grilles from the muddy water. I tried searching a while ago on google and people were suggesting Q tips or tooth picks to clean each hole individually. I didn't care that much so I left it. Got bored and decided to try something else today. I used some foaming vinyl cleaner and a stiff bristle brush and it came right out. The pic below of the dirt is actually the cleanest one there was, the rear ones were completely brown.Before
After
Supplies
So if you have this issue and want to clean it, this will work. Just mist the cleaner on so it doesn't damage anything. This may have been common sense to many people but if you're like me then here you go.