Oh, ouch! That sounds like bad valve linkage or a rod/ rod wrist-pin, so sorry.
I have 2,000 miles on my 2013 Hemi, it came with 5w-20w oil and in the recent chilly mornings here in Utah, it sounds a more like a car's diesel engine idling, a bit of clatter, which disappears when it warms up.
Best of luck, time to test your warranty. If anyone looks left or right before helping you, hire a lawyer. Don't waste your time with the Better Business Bureau or consumer advocates in your state government. For a couple hundred bucks, a good lawyer can send one letter that will cut through the bs. If it comes to being forced to file an actual suit, name the dealership owner, the service manager and general sales manager as defendants. I can almost guarantee the dealership's attorney will call your attorney to stop the suit and settle this before it goes any farther.
Best wishes, guy, seriously.