Well, before dropping the car off this morning I wanted to inspect their previous work to make sure I wasn't giving them crap for an unrelated problem. Both of the valve covers looked clean, but the cap for the oil filter is leaking a surprising amount of oil. I guess that explains the new rattling sound coming from the serpentine belt until the car warms up. (Oil was pouring right onto the belt.) Once they resolve this issue I don't think they'll be touching my car again.

-Spencer