As someone who hikes mountain trails instead of riding them, I very much appreciate the mountain bikers who have bells that jangle automatically with every bump or dip or turn. There are many blind hairpin turns, not to mention bikers who approach from behind going downhill at breakneck speed.
In my locale, hikers have right-of-way over cyclists, but as a courtesy I step off the side of the trail and let them pass IF I KNOW THEY ARE THERE.