exhaust components is a lifetime (muffler, cats, etc) on their smaller vehicles IIRC. I wish I had known about the warranty in 2010! That would of been nice!
Here is a script from Toyota:
Which parts does Toyota cover under the Lifetime Guarantee?
The Lifetime Guarantee covers Genuine Toyota...
Mine has gotten worse, if I put my head by the driver wheel it sounds like a diesel. It's gotten VERY loud. I can hear it with the windows up leaving a stop sign. DT's are on the way soon.