This topic has been beaten to death, however I agree with rchelial, if it was a design flaw then every Raptor V1 should woof. I've burned more gallons of fuel than I care to count through my R30 and R50 V1's, I've never had a "woof" or "wahwah". If you are having problems with "woofing" try one of the new reinforced pitch control arms for the V2, the new plastic one not the over priced metal arm. Also make sure you have your collective servo mounted solid I use the servo mounting plates they really keep the servo from shifting around.

Servo Mounting Plates