Yesterday I took my car to Hyundai. My car was making a weird noise around 1,800 rpms under load. The tech took a ride with me and he said he knows whats making that sound. He said my intake valves needed to be cleaned. I doubted him and said that it cant be because I use shell gas and mobil and exxon gas 90 percent of the time and they are all top tier fuels. And also I used tectron cleaner every 10,000 miles so far because sometimes I cant get top tier. He said trust me these di engines are known to gum up with carbon. Well I said okay do it . He said he was gonna use bg44 intake cleaner and do a fuel system flush. Well it worked the sound was gone and the car does have more pep. I wasn't happy when I got the bill because I don't believe that should be considered routine maintenance but whatever. I mean the tech actually said its a known problem. Well if its a known problem shouldn't Hyundai pick up the tab. Anyways the thing I was wondering is if I should change my oil today because of it. ID hate too waste the oil I just changed a week or two ago. Also my veloster only has 41,000 miles on it and needed a cleaning. Its obvious that Hyundai hasn't worked out the carbon problem on there di engines. Also I guess using top of the line synthetics 5w30 flavor doesn't make a difference on carbon on the valves. I change my oil and filters at 3,750 because of the di engine. But I guess that doesn't help either. From now on ill be using tectron every oil change. Also the tech after going for a test drive with me said I should get on this car and rev it out sometimes. I babied this car since new. Well I guess there is nothing we can do as owners of these di engines. If top tier gas and using syn oils doesn't work even with a tectron dosing here and there then I don't know what will.