I refuse to call blow off valve cute flutter noise "compressor surge." Compressor surge is bad when the turbo is loaded up, when there's say 25-40psi of pressure in the manifold/turbine housing. It sounds like a hammer because the turbo is turning 130,000rpm, with 300* compressor outlet air temps.
When the motor is in vacuum and you get the BOV flutter noise, no damage is occurring because the turbo is "freewheeling" and the noise is primarily from a partially open valve and its just air noise...not the compressor working as a brake.
Discuss if you want, I've read a lot about this because I'd rather have my BOV closed in cruise than sucking in sand.