2014 Silverado, just purchased, whining and running lean.

[Revolution76]

I just purchased this truck (2014 Silverado LT 5.3 113,000 miles) literally this afternoon. It was fine at the place I bought it. However, I drove about 4 hours running errands and noticed the check engine light kick on, I got out to assess the situation and noticed a loud whining/buzzing noise coming from the engine bay (similar to a bad power steering pump or a tank mounted fuel pump in other vehicles) accompanied by a lean smell from the exhaust. I assume, or hope, this is the high pressure fuel pump and not the oil pump. Oil pressure values are within normal ranges (for now). The sound is louder in the back of the motor by the cab, but I can't identify if it is in the upper or lower part of the motor. Dealer has many clauses in limited warranty and I am almost certain he will jump through one of those loopholes to avoid covering repairs if the problem is severe, although he has many good reviews. I will read CEL code in the morning for more insight, for now any help would be appreciated greatly. Is there any common cause for these symptoms and if there are, how can I diagnose them through a process of elimination or other means?

Edited March 3, 2022 by Revolution76