220PS groaning noise under braking on motorway.

Hi I just wanted to know if anyone else has experienced a groaning noise and slight vibration from brake pedal when slowing down from 80/75mph. I noticed this last two weeks and car has already been into Skoda dealers last mo the after I fitted new discs and pads on the front and new pads on the rear as before this the car was chewing through the rear pads and after inspection by Skoda they said nothing wrong with car or rear discs or calipers. So they said to come back in 2k miles. However this noise I don't know where it is coming from it is very annoying.