After a repair on my 2.0L 2014 Mazda 3 (31,000 miles) by the Mazda dealership my engine has been having some very concerning sounds. The one I'm most worried about and that has recently popped up is a "jackhammer" type sound. It's almost like metal on metal or as if the engine had no oil. It does have plenty of oil. The repair they did was a oil valve control (gasket was leaking) along with a "seal" and a new head cover gasket. It's pretty concerning. I have video of the sound I will put on at the end of this paragraph. The intake also has this sort of hiss as if it was letting go of air pressure. I honestly don't get it with this car. So many issues so far (Been to dealership at least 6 times). Anybody have any ideas?