Mine did that when i had a big HKS blowoff on the stock turbo setup. if you put your hand in front of the turbo and rev the motor( not too close) you will feel air pushing of the turbine inlet. my guess is the blowoff wasnt sized correctly or it was set too tight.
right now with the T88-34D and a 60mm Tial blowoff it does not do it. just hear a swhish sounds coming from the blowoff, no flutter.