I was driving last night with the radio off to check for rattles after my speaker install (from last week) to make sure I got every thing buttoned up tightly. As I was gently accelerating I noted a beeping buzz that comes from the passenger area when I hit around 4200 RPM. It does it accelerating and decelerating and will constantly beep if you hold it at the correct RPM. My rev light is set at 6200 RPM. Any clue what this beep is? TCS override? Variable engine controller?