2003 Chevrolet Silverado noise coming from engine bay

Lately I have noticed a buzzing or clicking noise that comes from the engine bay, can be heard in the cab while driving but is more pronounced when idling with hood up. Sounds like a solenoid opening or closing and comes and goes in about 2-5 second intervals. I haven't heard it before and I listen to my vehicles as I'm driving them. Its a LB7 duramax and I'm kind of new to diesels. Any ideas would be appreciated. No codes, idles great, starts great, runs great, just an annoying sound I haven't heard before.