This engine is noisy to start with but you will hear the rattle on the passenger side, low in the engine compartment near the firewall. When it first starts out, it sounds like the serpentine belt tensioner is the culprit. The best way to know is to remove the serpentine belt, then start the engine. The water pump is driven by the timing chain, therefore it will continue to turn and rattle.

Here's the big beef. This engine is also known for the timing chain tensioners to fail at 100 - 125K miles, therefore most shops suggest you to just buy the kit w/ the water pump and timing chain replacement ($550.00) and pay them a DAYS labor to install it ($800 or more). Thinking of doing this work DIY? Look up a video at YouTube first to make sure you're up to the task and have the special tool(s) needed. It's a lot of disassembly between the engine and firewall, where it's hard to work, which is why they charge a full days labor. This is supposed to be one of the better revisions of this Ecotech 2.4L, but I think a water pump failure at 75K and a timing chain overhaul at 125k is too premature, when your competitors like Mazda CX-5 are getting 200 -250K miles of trouble free usage.