Ford Fiesta MK6 deep moan with release of accelerator

Question

While driving my Fiesta on the motorway I noticed that at around 3000rpm/70mph that if I release my foot off of the accelerator completely (I just let the current momentum propel me forward) the following happens after about 2 seconds:

The engine feels like it suddenly grips something. The same sort of feeling when it engages with different gears. 
A loud deep hum noise kicks in for the duration my foot is off of the accelerator.

When I put my foot back on the accelerator everything goes back to normal.

Was wondering if anyone had any idea what it could be?

Edit 1

The clutch is riding quite high with about 1-2 inches of clearance when it engages.

Edit 2

Just some further information from comments on the car:

The car is a 1.2 L Ford Fiesta Mk6 Zetec 2006 UK Model.
I don't do much motorway driving so I am not sure if this is new or not. I only get a sound 2 seconds after I have let go of the accelerator. At the time I am doing nothing to the clutch. 
The clutch is still firm on depression with no noises or spongey-ness. The clutch isn't slipping either
I think the sudden grip could be engine breaking but the deep hum is so loud it doesn't sound like it should be there.
The exhaust has recently been fully changed by a local garage who are very good.

Sam Basso · Answer

Not enough rep to comment and ask for more info so I'll wing it. No idea on anything outside of the production year range and that it's likely a UK model.

Describe the engine and trim options for a better answer. Also describe if the humming is speed-based, varies in pitch, or is accompanied by vibration for a more accurate answer.

Current guess is a bearing. Isolate and rule out transmission problems by checking the fluid level/condition and observing shift behavior. Is shifting notchier/sloppier than it used to be? Does this persist after you check the clutch cylinders (and inspect the pedal itself?)

If its not clutch related and it makes the car vibrate it could be a mount. a deteriorated mount could pitch the spinney parts at odd angels and create some noise and vibration.

Not clutch related and no vibration could be a bearing anywhere in the drivetrain but more likely in a wheel. Bad wheel bearings hum and impede coasting, so do bad gears and bearings in differentials.

Could also be a poorly mounted exhaust rubbing on something underneath. Is the vehicle stock? Cant rule out an electric pump or other moving part either. current evidence indicates a bearing somewhere. can you lift the car and have someone listen around the vehicle?

Current best advice is to take it to a garage.

Ford Fiesta MK6 deep moan with release of accelerator

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