A hissing noise, sort of like escaping air, can be heard on the drivers side of the car ( 2001, S60 2.4 Turbo)

the noise stops when I press brake pedal. started a few days ago and worse now.

any specific ideas?

thanks

 

could be a vac leak, check all your lines leading back to your brake booster
or could be a leak due to pressure from your turbocharger, does the sound get worse if you really womp on the gas?