busted ballast causing my grow room to overheat?

I have a http://www.greners.com/grow-lights/ballasts/brand/nextgen/nextgen-600w-400w-hps-mh-ballast.html

nextgen 600w ballast and its been good for a couple of months now but recently my room is overheating and there are less plants in there now and airflow is the same. i can't figure it out, im thinking that it might be the ballast because i hear nextgens break after a few months. it has a weird sound when it's on and if i tap it it gets louder

edit: the ballast is outside of the closet, so i was wondering if it was causing the light it self to overheat?

its probably because of higher ambient temps. it is summer now.
if it makes a sound it means the fans are off-balance, get a C02 "squirt" can and clean the dust off the fans.
the ballast wont make the bulb run hotter. also the fact that there are less plants transpiring (breathing) would lead to lower humidity, and therefore higher heat.
if heat becomes a problem you can run your 600w bulb on the 400w setting. (it will put out 400w worth of lumens.)