My dads 2007 GMC Sierra classic making a werid clicking sound every once in a while, mostly when hill climbing.Maybe even when shifting gears(its an automatic) We dont know what it is and want to know what it is. If anyone else is incountering this problem, let us know what you think it is. I personally think its the electric fans turning off. My dad thinks a relay switch or some sort of shifting switch. What do you think?
