How can I fix burping noise(Avensis 1.8T3X 04)?

My 04 Avensis T3X 1.8,makes a low "burping"noise when accelerating in second or third gear,a guy at my dealers let it slip that it was a common fault in that model yet the dealers are refusing to acknowledge the problem blaming my "style of driving"!My car is well maintained and serviced regularly yet I can,t seem to make any headway with this problem.Can anyone help or suggest anything?