Ok, am I reading this right? When a creature or object touches the wall, 3 things seem to happen.
1. If it's a creature, it takes 2d6+1/caster level in sonic damage, no save
2. If it's a small or smaller flying creature or a small-ish object, it bounces off.
3. When 1 or 2 occurs, it triggers a "burst of discordant noise deals 2d4 points of sonic damage to creatures within 10 feet of the triggering object or creature". No save
If that's the case, what happens if, say, I use telekinesis to send "up to 15" objects flying at the wall? Even though they will all bounce off, it seems that each will trigger the 2d4 sonic damage burst from the wall. 30d4 sonic damage, no save. 2 casters working in tandem could deliver 2d6+caster level + 30d4 sonic damage, no save, and still have the wall in place. And as the number of telekinesis users increase, the damage just goes up.
BUT that's not where it ends. If you get an enemy into a pit (one of the pit spells) and overlay this wall of sound over him within the pit, and drop a decent-sized item in...assuming that bouncing off the wall proves insufficient to propel the item out of the pit, would it just keep bouncing up off the wall, falling back down due to gravity, bouncing up, falling back down etc for an infinite chain of 2d4 sonic bursts? What about if I emptied a bag of marbles into the pit? Say there were 30 marbles in the bag. 60d4 sonic damage with no save?
Or even better. Sleet storm. A storm of icy bits flying around in a cylinder effect. Suppose you cast wall of sound so that the enemy is within the wall (which the spell permits you to), then overlay a sleet storm over it. How many little icy particles will be bouncing off the wall? How many little bursts of sonic damage will we be dealing with there?
It is definately prone to abuse.
Since it does not specify anything about several items at once, my ruling would be that the wall only makes one burst of discordant noise per action.
RAW does not support whether or not this is the case, and it seems like an decent fix for the problems the spell could cause.