My ecoboost makes a chattering type of noise when cruising around 2k rpm and the engine is being put under a load (for example starting to pull a hill).
If I left off the throttle it will stop and immediately run the engine hard it wont do it again until I start cruising again. The best way I can describe the sound is it is very similar to the sound an old carbureted engine would make when it is spark knocking. I thought it was bad gas and have been switching locations where I buy it from but have not found a direct connection. The sound is not persistent it will be there for a few days and then may be gone for weeks or just a few days. It is very frustrating.