Sound different driving before car is warmed up?
 

Hello,

I've always wondered if everyone else's brz sounds slightly strange when driving before it is fully warmed up.

I hear a whiny noise when I accelerate, almost like a mini supercharger...most likely source is the belts.
The exhaust note is a lot more raspy and dull sounding compared to the usual deeper note rumble (I have UEL)

But once the car is warmed up, all of these disappear. What is the cause of this?

The predominant cause of the engine sound and resultant exhaust note prior to the engine reaching operating temperature is negative valve overlap combined with an initial high idle. Simply put, NVO helps warm the primary catalytic converter, lowering tailpipe emissions. See this patent for more information: http://www.google.com/patents/US6394051

Thanks for taking the time to reply.
Cool, didn't know google had a patent database haha.

I believe NVO is the negative ignition timing that can be found on the ignition timing post start timing with Romraider. But once the car starts to more, it switches to the primary base tables which does not seem to be affected by temperate. But i didn't consider until now that there are most likely a bunch of other timings based on temperate that would change the resulting exhaust note.