grinding noise on the highway?
 

Hi all,

Thanks for having me and thanks for taking the time to read this and help! Any and all input is appreciated.

This morning (roughly freezing temperature - nothing out of the ordinary after the brutal winter we just had) got onto the highway to head to work and set the cruise control (as normal) at approx 110km/h (65mph) and after several seconds heard a distinct, quite unpleasant grinding noise. It was loud enough to be heard over the heater and radio. Turned the heater and radio off to listen closer and didn't like the sound of it - sounded like metal on metal. There was no different feel in the floor, pedals or steering wheel. As soon as I turned cruise control off, the noise disappeared! Turned cruise control back on, and the noise returned approx 5 seconds later. If I continued driving along normally and sustained a certain speed, the noise would appear after 5 seconds again and only go away once I lifted off the gas or coasted down a hill... Very bizarre. Once I got to work and poked my head underneath didn't immediately notice anything out of the ordinary - no funny smells or anything...

Hoping someone with a bit more knowledge than I have could provide some insight before I bring it to the dealer and know what I may be getting into...

Background info:
2011 FX4 ecoboost, crew cab. Stock, no modifications. Approx 134,000km (~80,000 miles)

Thanks!

In case anyone is still following this (and in an attempt to help anyone who may have the same problem) - my brake vacuum pump was becoming worn out (caused a loud humming/whirring hair-dryer type noise on startup for 60-90 seconds) and due to the loss of vacuum, the 4x4 was partially engaging causing said grinding noise on the highway. Ford replaced the vacuum pump under extended warranty, no more funny noises!