I have a 2015 Sonic 1.4T with around 21,000 miles on it and with no mods at all. I have only had the car for a month or two now and I have discovered a noise from the engine compartment but only at around 4000 RPM. The noise is a very high pitched noise almost like the blowoff of a turbo only more metal sounding. The first time I took it to the dealer they said that they could not replicate the noise, so when I got it back I started to experiment with speeds and RPM and was able to replicate the noise if while in manual mode I hovered the RPM around 4000 in 3rd gear. I took it to the dealer and replicated it for them and they heard it as well and mentioned it didn't sound normal. I want to also mention that the noise only happens when the ac is on and will also happen in automatic mode when accelerating on to a freeway or similar. The dealer is unable to isolate the problem and when they called GM engineering they were told to compare it against another 2015 Sonic which they did (a 2015 with only 100 miles on it) and when driving it the same way, it made the noise as well. I was told that it must be a noise that this model makes and that there is nothing that they could do. They said that it might be the ac coolant going by a valve or something to that affect. I've worked on and driven my fair share of cars and I have never heard a noise like this come from an ac system that wasn't broke. I wanted to know if anyone on here has heard that type of noise from their car also. This is my second GM car and the second time I've been told that something that I thought was not normal was just the way the car is....the first time was when I had the low oil light come on in a brand new Spark and I was told that it was designed to burn a little oil. I told them "then that is a poorly designed engine". My faith in GM cars is slowly waning.
