My new 08 Corolla has a growling sound when going slow, like 1 to 3 mph. If I am on a slight uphill incline the motor really growls. I don't recall it doing that on the test drive.
I have a 07 Corolla and mine did the same thing especially 1st thing in the a.m. when I first got it, then it started with a no start condition which the computer needed to be replaced under warranty, it doesn't growl now I don't know whether it was associated or not. It has 7500 miles now. It seems liked it took it a long time to break in.