Metal Halide

Have 150W 4300K ARCADIA (Pendant) MH Lighting. Problem is:

1) sometimes the light would go off and comes back say 30 mins.
later. I was told that MH is very sensitive to changes in
voltage. A slight drop in voltage would shut off the light.
Is this true?

2) the ballast sometimes hum, but now it has stop. Now it's
the pendant's turn to give a very annoying hum. How can this 
be rectified?