Most decks across america are constructed using pressure treated pine. That being said, most deck railing spindles are also the same pressure treated pine. Chances are these spindles are split or warped.
Relax... No need to replace your whole railing system. I have a great, inexpensive alternative.
Remove all of these spindle, pressure wash and sand down your upper and lower rails. You can treat these rails with some kind of stain or sealant.
Chances are, the space between you upper and lower rails is 32".
If this is the case, you can simply add an aluminum face mount baluster.
I would recommend either of these 3 options.
By taking these steps and replacing your balusters, It will give your railing the much needed facelift that you where looking for.