I live down the 57 freeway from you and have the same crappy water you do. 11 years for a water heater is remarkable in SoCal. I've replaced two in my house in the past 15 years. No matter how bad your pipes are, I'm sure the water heater is toast either way. The noise is likely from your water heaters- at least is was for mine.
The good news is that new water heaters are far more energy efficient than the old ones and I saw a drastic decrease in my gas bill. It also heats the water up a lot faster too.
Because you cannot eat a salad with a spork.