My Expedition's got this wierd noise

I recently bought a 2000 Expedition 4WD 5.4 L. It’s got this wierd noise that I think is possibly vacuum related, etc. It’s a ticking noise that only occurs at startup, lasts until I advance the throttle and then it goes away and never reoccurs until I let it sit. Sounds like it’s coming from the right side of the engine compartment and varies with engine speed until, like I said, it goes away when I give it more gas. Seems like it’s related to vacuum.