My car went into limp mode on my drive home went away then showed up a few days later. When I cold start my car there is a loud whistle at idle. Also when the engine is running it sounds like an air leak in the engine bay and it proceeds to empty out after the engine turns off. I'm assuming it's a vacuum leak. Also when i put my car in sport mode the exhaust pops are much louder than normal. Any help is appreciated. (2012 countryman s)

 

follow the hissing sound and see where it takes you. as you mentioned, possible vacuum leak somewhere. look for it and let us know what it was

 

I had a loud hiss and whistle after checking my air filter. Turns out I hadn't put the airbox back together properly, and air was leaking. Unfortunately rockauto sent me the wrong filter, too.

 

Im 90% sure its your valve cover. Very common. Sometimes it sounds like the whistle is coming from your trans. Is your motor the n14? Definitely take a look at your intake system first. But it's most likely your valve cover