Dumpvalves are a waste of time in most cases.

And 2 DVs are likely to give you LESS noise than 1, as the pressure is shared then.

Ive tried it too When i had my first reno5 i had a DV (1998, they were COOL then, not 2005 ) and then we fitted 2, made no difference, maybe slightly quieter, so for a laugh we put another one on we had lying around, that deffo made it quieter than 1.

Id never fit one unless needed, as chatters far better.

I cant decide wether to risk running without them on my GTR as its gonna be running silly boost
My main thing about running them isnt that i dont like the noise, im worried theyl be rising slightly from their seat at full boost, ie leaking slightly, i think its FAR more common than you think, and will overspeed the turbo like fuck and lose you power even if its same boost.