The egg rolls. In a large bowl, whisk together the salt, black pepper, fish sauce and egg. Add mushrooms, glass noodles, onion, scallions, shrimp, and ground pork and stir until combined. Set aside.
Carefully separate the wrappers. To prevent them from drying out as you work, keep a barely damp paper towel over the unused wrappers. Place one wrapper on a clean surface so it's a diamond. Put 2 heaping tablespoons of the filling on the lower third of the wrapper and use your fingers to shape the filling into about 4-inch log. Fold the bottom edge over the filling, then fold in both sides and roll tight. Brush the other side of the wrapper with beaten egg white to seal the edge. Keep rolls chilled, and loosely covered, until ready to fry.
Heat 1 ½ inches of oil in a large pot over medium-high heat to 350°F (175°C). Fry rolls in batches, adding as many as can fit comfortably in a pot, without crowding, for 5-7 minutes until golden on all sides. Remove from oil and drain on paper towels.
The sauce. In a small bowl, combine the lime juice, rice vinegar, sugar, and water and stir until the sugar is dissolved.
Start adding the fish sauce tablespoon by tablespoon, adjusting the amount to your taste. When satisfied, add the chiles and garlic. Allow the sauce to chill to room temperature and serve.