2006 Volkswagen GTI Loud Siren Sound

Hello,

I have a 2006 VW New GTI 2.0 w/turbo and 84,000K. A few months ago the vehicle started making a very loud and constant high pitch siren sound. As soon as the car is started the sound begins and remains no matter which position the transmission is in. Once you step on the accelerator and turbo boost kicks in the sound disappears. Immediately after letting off the accelerator the noise returns. I was told the noise was coming from the front of the transmission and ok'd a tranny flush and fluid replacement. No luck.I was also told it was the timing belt and another mechanic said belts, pulley and or tensioner. Please help me! I am at wits end. I think its the turbo system?