Metal Halide Help Please (loud buzzing noise)

[jabberjaw]

Hi everybody,
this is probably a really simple question, but as a Metal Halide noob I need a bit of guidance.
I purchased a second-hand 2xMH/2xT5/2xLED combo lighting rig - everything was going fine until about a month ago when the unit started making a very loud buzzing noise. This usually quietens down after a couple hours, as it is extremely annoying it is a problem I would like to get fixed ASAP.
Im pretty sure I have identified that the noise coming from one particular MH light/ballast and have noticed a slightly higher level of vibration coming from that area.
Does anyone know the source of this loud buzzing and what I need to do to fix it?

 

[Manzanitadude]

Before you go tearing into it, is it a noise coming from the a cooling fan or is it from the fixture itself? Maybe something worked its way loose and needs to be tightened down? Are you able to run just one side at a time to determine where the noise is coming from? Sometimes ballasts get noisy before they go out. If it is a ballast, I would have someone with some electrical experience replace it. MH bulbs sometimes make wierd noises too- how old are they?