Weird sound from engine

[JayZh]

Hi friends, 

i am driving CLA180 and recently i notice some weird sound from engine (maybe). i dont know how to describe the sound , but it sounds like blow whistle. Especially when the speed over 90km/H, the sound will became more clear... even i release the accelerator, as long as the speed above 90 , the sound will contiune until the speed below 90 km. 

I have checked with my WS, but they couldnt exactly diagnoses what problem is and the sound really drive me nuts... 

Can some experts here share with me if you have the same experience before ? And how can i fix it ?

thanks in advance 

[darksaint]

Could it be wind noise from the windows cos CLA coupe design is more obvious. 

Or the aircon pipe sound which I encounter before. 

[JayZh]

Thanks bro