No, I havent done an engine flush, what does an engine flush consist of? I also usually use Quaker State High Mileage Formula 10w30. Another thing about that noise, 9/10 it goes away when the engine is warm and usually (not always) only happens on cold starts. It's not as loud as it sounds on the WAV file but loud enough to where you can hear it in the car. Also, if you listen to the idle rev, it kinda coincides when the throttle is pushed. One more thing, if you listen to the exhaust, after it revs each time you can kinda hear a grinding noise, you have to listen closely.