I was driving my 03 WRX the other day at about 70 mph, not pushing it much at all and all the sudden I notice my turbo is not spooling. I hear a kind of groaning sound in place of the sound of the turbo. I checked my oil, which was a little low, hoping that would fix the problem but still the same noise with no spool. The car still runs and idles fine. Where should I start? Any help would be greatly appreciated.