Own a 2015 3.5 EcoBoost. Since day one a slight rattle/vibration could be heard at 1 rpm and louder when going up hill. Dealership originally said it was normal on 2015 model which I figured was not true. My guess is when they drove they were hearing the whooshing from an aftermarket item put on by original owner and thought I was nuts. Frustrated switched dealerships and drove with mechanic, he heard and 2 days later picked it and was told fixed. Driving away I heard the noise again but was to frustrated to walk back in so cooled down. At this point it goes back next week and I duplicated the sound. Any thoughts will be appreciated before I walk in there. Have a video but cant upload for some reason.

 

Made this recording , appears to be between wheels back of engine

 

Sounds like an exhaust heat shield rattle. Does it change as the exhaust warms and cools? Pretty easy fix, usually it just requires a slight tweak. The tac welds will break over time, and get worse.

 

It is constant to the rpm. Start up or mid stream always at about 1 rpm. I duplicate by holding brake and then fluctuate gas to the 1 rpm. They actually changed out a part (intake tube?) which wasnt covered under my warranty and was not the source of issue.
I appreciate the input as I hate going in not knowing.

 

My 2016 2.7 has this same sound. I thought it was my skid plate, took it off, but still have it. I can also replicate it by braking and getting my RPM's at 1k. It sounds terrible when I am at a drive thru and it echos off the building. Would love to figure out what it is...

 

On my 15 3.5 EB - the cross pipe from the driver side exhaust (behind that felt transmission cover). The factory welded on "clamp" broke and the heat shield was rattling the same way. I just tossed a worm screw clamp on it and it went away.