Diagnosis
Hard water scale deposition. The water heating element is creating mineral precipitate. The most likely cause is exhausted rinse aid or incorrect detergent type.
How to Fix It
Ensure the rinse aid dispenser is full. Set the rinse aid dial to setting '4' or '5'. Use a dishwasher detergent formulated for hard water, not a multi-purpose tablet with built-in rinse aid. Run a clean cycle with a commercial dishwasher cleaner to dissolve existing scale.
If That Didn't Work
The internal water heater may be failing, not reaching the correct sanitize temperature of 120°F. This prevents proper detergent activation. Check for lukewarm water at the end of a cycle.
Heads Up
Using liquid dish soap or hand-washing detergents will create massive suds and leave residue. Use only products labeled for automatic dishwashers.