Sounds rough when on full steering lock?

[Awkward kid]

When I stick the car on full lock the engine sound like a bag of nails? It's a 150 diesel lump. Any ideas?

[John35]

There is a release valve. When on full lock the pressure is somewhere near 800psi in the power steering system. The noise is the system letting some pressure "out". You never stay on full lock longer than necessary.