I have been getting a noise for a couple of months now, which only seems to occur when I am on the motorway or carriageways or anywhere I am going around 50mph or above for a consistent amount of time. Sounds like a whirring noise coming from the direction of engine, but it more a of a high pitch constant noise which gets stronger if I press the accelerator and dims down when I let go of accelerator but you can still hear it. It is quite loud and rather irritating. Not sure if anyone has any ides what this could be? Fiesta ST MK6.

Thank you for any help.