First off what cfm is your air filter. The sound could be caused by a couple things. First off is Turbo Surge, the other would be the turbl trying to suck air through your filter, the third is just the waste gate bleeding off the extra boost.
Ok lets look at turbo surge. Surge occurs when the extra air in the turbo has no where to go. So it goes back out the inlet. If the surge is bad enough it will cause turbo stall.
CFM and the air filter, if the cfm is not high enough the air filter is being to restrictive. Thus causing a constant whooshing sound of air. That whooshing sound is nothing more then air getting pulled through the air filter. A way to stop this replace the air filter with a higher cfm air filter. Remember the size of the filter doesn't matter. What matters is the cfm number.
Now the third thing I was talking about waste gate bleed off. This is occurs when the psi level is reached and the waste gate opens up. The waste gate will remain opened until the psi level is lower then the rating of the wastegate.
Now to determine what your problem is. Well you have the banks wheel, which is nothing more then the wicked wheel. So that should prevent your surge. But it does not always prevent it or stop it. So you may want to look at the bigger compressor housing.
Air filter you did not mention what your cfm of your current air filter is. I know mine is around 900cfm. I do not have this problem. So like I said your air filter can be big but the cfm numbers have to be high. But do not sacrafice the filtering of the filter for higher cfm.
Waste gate, well if it is opening often, or staying open for long periods of time. Then you may want to look into a different waste gate.