My ballast is making wierd ping noise when niot turned on

Got 4 1000 watt hps ballasts connected to a 120/240 volt cap timer and for some reason when the lights are off every few hours or so i hear a ping type noise like somethings flicked the side of the metal casing. I know what to do to isolate it but Its been happening for a while now and no fire or fried bulb. But I assume this happened to someone else. What is it, what did you do, and what brand was it? Thanks

Magnetic Ballasts right?
im guessing the metal is contracting as it cools?
have you ever heard the engine block of a car *ping* when its cooling down from a long drive?
im thinking its probably the same thing.
our 600w digital ballasts run silent, even when firing up/cooling down.

Maybe your ignitor is about to bite the shit, mite wanna post this in grow room setup section

max316420 said:

Maybe your ignitor is about to bite the shit, mite wanna post this in grow room setup section

Click to expand...

but the sound is happening when the ballast is off, meaning it shouldn't be the ignitor, unless your CAP timer is having issues? (question, not statement)

hmmmm I'm actually shocked ive never burnt a house down so i'm the wrong one to be giving advice.. there was a guy on here that was an electrition giving help but don't know if he is still on here. I'll look and see if I can find his post offering help