My MY97WRX has a HKS induction kit, Magnex single dump downpipe, Magnex 6X4 backbox. With the standard dump valve in place there was a noticable delay in pickup after a high rpm gear change, a recent thread suggested it was the OEM dump valve not releasing enough pressure and was stalling the turbo, I have picked up a VTA dump valve, this has cured the apparent turbo lag, but it has caused the overboost protection to come in at nearly every full throttle acceleration attempt. I can feathure the throttle to stop this happening. I have noticed a slightly dull but loud screaming coming from the turbo area just before overboost is about to happen. Could this be a problem with the waste gate? or is it the turbo overspeeding?. Any thoughts would be appreciated.