Mine doe's this aswell, i have the Bailey also. I thought it was o.k as my theory was that as your not creating enough boost low down the pressure isn't enough to fully open the valve, hence why you get a different noise and the valve doesn't open fully. My old starlet used to do this as well, but that was a different valve but i cant remember the name, sorry.
This might be wrong, but it could help.
Rob.