diff --git a/libraries/octree/src/Octree.cpp b/libraries/octree/src/Octree.cpp
index 808b49d475..5d25f0c164 100644
--- a/libraries/octree/src/Octree.cpp
+++ b/libraries/octree/src/Octree.cpp
@@ -592,6 +592,7 @@ bool findSpherePenetrationOp(OctreeElement* element, void* extraData) {
     if (element->hasContent()) {
         glm::vec3 elementPenetration;
         if (element->findSpherePenetration(args->center, args->radius, elementPenetration, &args->penetratedObject)) {
+            // NOTE: it is possible for this penetration accumulation algorithm to produce a final penetration vector with zero length.
             args->penetration = addPenetrations(args->penetration, elementPenetration * (float)(TREE_SCALE));
             args->found = true;
         }
diff --git a/libraries/particles/src/ParticleCollisionSystem.cpp b/libraries/particles/src/ParticleCollisionSystem.cpp
index def6768e46..8eb525a388 100644
--- a/libraries/particles/src/ParticleCollisionSystem.cpp
+++ b/libraries/particles/src/ParticleCollisionSystem.cpp
@@ -79,8 +79,8 @@ void ParticleCollisionSystem::updateCollisionWithVoxels(Particle* particle) {
         // let the particles run their collision scripts if they have them
         particle->collisionWithVoxel(voxelDetails);
 
-        collisionInfo._penetration /= (float)(TREE_SCALE);
         updateCollisionSound(particle, collisionInfo._penetration, COLLISION_FREQUENCY);
+        collisionInfo._penetration /= (float)(TREE_SCALE);
         applyHardCollision(particle, ELASTICITY, DAMPING, collisionInfo);
 
         delete voxelDetails; // cleanup returned details
@@ -134,7 +134,6 @@ void ParticleCollisionSystem::updateCollisionWithParticles(Particle* particleA)
 
             _packetSender->releaseQueuedMessages();
 
-            penetration /= (float)(TREE_SCALE);
             updateCollisionSound(particleA, penetration, COLLISION_FREQUENCY);
         }
     }
@@ -184,8 +183,8 @@ void ParticleCollisionSystem::updateCollisionWithAvatars(Particle* particle) {
                 }
                 // HACK END
 
-                collisionInfo._penetration /= (float)(TREE_SCALE);
                 updateCollisionSound(particle, collisionInfo._penetration, COLLISION_FREQUENCY);
+                collisionInfo._penetration /= (float)(TREE_SCALE);
                 applyHardCollision(particle, elasticity, damping, collisionInfo);
             }
         }
@@ -216,8 +215,8 @@ void ParticleCollisionSystem::updateCollisionWithAvatars(Particle* particle) {
                     }
                     // HACK END
 
-                    collisionInfo._penetration /= (float)(TREE_SCALE);
                     updateCollisionSound(particle, collisionInfo._penetration, COLLISION_FREQUENCY);
+                    collisionInfo._penetration /= (float)(TREE_SCALE);
                     applyHardCollision(particle, ELASTICITY, damping, collisionInfo);
                 }
             }
@@ -293,18 +292,20 @@ void ParticleCollisionSystem::updateCollisionSound(Particle* particle, const glm
         velocity -= _scale * glm::length(gravity) * GRAVITY_EARTH * deltaTime * glm::normalize(gravity);
     }
     */
-    float velocityTowardCollision = glm::dot(velocity, glm::normalize(penetration));
-    float velocityTangentToCollision = glm::length(velocity) - velocityTowardCollision;
+    float normalSpeed = glm::dot(velocity, glm::normalize(penetration));
+    // NOTE: it is possible for normalSpeed to be NaN at this point 
+    // (sometimes the average penetration of a bunch of voxels is a zero length vector which cannot be normalized) 
+    // however the check below will fail (NaN comparisons always fail) and everything will be fine.
 
-    if (velocityTowardCollision > AUDIBLE_COLLISION_THRESHOLD) {
+    if (normalSpeed > AUDIBLE_COLLISION_THRESHOLD) {
         //  Volume is proportional to collision velocity
         //  Base frequency is modified upward by the angle of the collision
         //  Noise is a function of the angle of collision
         //  Duration of the sound is a function of both base frequency and velocity of impact
-        _audio->startCollisionSound(
-                    std::min(COLLISION_LOUDNESS * velocityTowardCollision, 1.f),
-                    frequency * (1.f + velocityTangentToCollision / velocityTowardCollision),
-                    std::min(velocityTangentToCollision / velocityTowardCollision * NOISE_SCALING, 1.f),
-                    1.f - DURATION_SCALING * powf(frequency, 0.5f) / velocityTowardCollision, false);
+        float tangentialSpeed = glm::length(velocity) - normalSpeed;
+        _audio->startCollisionSound( std::min(COLLISION_LOUDNESS * normalSpeed, 1.f),
+            frequency * (1.f + tangentialSpeed / normalSpeed),
+            std::min(tangentialSpeed / normalSpeed * NOISE_SCALING, 1.f),
+            1.f - DURATION_SCALING * powf(frequency, 0.5f) / normalSpeed, false);
     }
 }