I don't want to sound paranoid, but I hear a slight whistle as well when driving my bone stock MCS 07. No whistling at idle and can hear it when revving, is it just the turbo? I recently had the CEL light on, but no code is displaying. When I went for the pre-purchase inspection, they told me the O2 sensor was literally hanging off. I assumed that after 1k miles it eventually crapped out. It doesn't sound like a valve became lose, am I just being paranoid? I haven't experienced any power loss or anything of the sort. I just want to rule out being something serious before I take it to a dealer or tech.