i maybe wrong guys, but there has been SO much on the so called flutter sound... HAving experience, i had a series 2 R33, and had the BOV really tight... It would flutter upto 4,000rpm... I had stock turbo, pod, fmic, zorst and was boosted to 11psi.. i had this setup for abt 1.5 years and drove with that kind of flutter for abt 40,000kms.. at the time my car had 110,XXX on the dash, and i have sold it.. i still kepp in touch with the guy who bought the car, and its still been fluttering and turbo is still in awesome nic..
theoretically, YES, flutter is bad cause its forcing air back through the turbo, however, it hasn't been proven ti damage the turbo nor the life of it... Alot of ppl have said that it WONT reduce the life of it and i agree with them because of my experience with it.. I have an s15 now and have driven abt 15,000kms with flutter with no probs..
Remember, if u import ur car from Japan, who knows what condition the turbo is in.. Just a thought.. Hope it helps!
Rob