The DV+ just makes a little mouse squeak when you lift off on part throttle, otherwise it's silent! It's very subtle though and you can't hear it with the windows up.
A for the tshhhhh blow off noises......there are tshhhhhh noises, and there are tshhhhhh noises! A big turbo with a big TIAL 50mm bov makes a cool noise, but a little turbo with little bov, not so cool!