Fiesta Mk-7 Zetec-S hum at 3000rpm

[alexavfc]

Hello all, looking for some advice on my Fiesta Zetec S- which on the whole has been a good reliable car

However recently I have noticed when I am approaching and hit 3000rpm, its as if this hollow humming noise coming from the engine as it is cruising along kicks in,  which is loudest when in 5th gear, 3000rpm 65ish mph. Its a hard to really accurately describe it however the car still drives normally, but I am concerned that this noise is getting progressively louder however its at its loudest when it is sat bang on 3000rpm.  I tried to get a video of it earlier whilst driving home whilst my phone was sat in its dock but it seems to have picked up more road noise

The car has just past 68000 miles, and is a 59 plate, appreciate its a poor description of the problem, but hoping somebody may know something

It has its service and MOT at the start of September, so I'm hoping it hangs on in there until then

Thanks

Alex