Ive got a 2 door Hatch Astra AH 2005 1.8 Manual and ive noticed a new whining sound when idle.

https://youtu.be/6FHbHUjCkLM

after i rev it idles fine then the noise comes.

i noticed it after i got a service. i had the timing belt done. i went back into the shop today and they checked it over and said the belt is fine, they took the drive pulley off and the noise still was there.

they said it could be the throttle body, im not sure what that is and how.

any other ideas?