shocking feedback

i have had it now with renault. Since last year(08/05/2014) i had a ping on my sandero,now the report they gave me is pathetic. According to them it is normal for the car to hear a ping sound as the engin is built that way. now the question is why did they done all sort of test in the 8 times my car was at the dealer(and the head was taken off twice),they could have just tell me its suppose to be that way. Its the first time i hear something like that. and apparently the conditions also play a role.I think its just a matter of poor product. i definitely not going to accept it and will make sure it will go to the right persons. so,all the cars is suppose to do it,because they talking of carbon build up, or is it just renault. the second question is if its suppose to be like that,why don't they tell the customers its doing it and why didn't it pings from day one,then i would definitely not buying it,but insted the sale is much appreciated.