I have an 08 LE with 45K on it. For the last several weeks it has made an odd engine or transmission "knocking" or thumping sound between 40-60 mph when I start to decellerate. There is no sound when I am accelerating and there are no issues with perfromance. I am worried it is an emerging engine or transmission problem. Any thoughts?

Never heard of that...I would get it to your local dealer asap!

Have you checked your ATF fluid level?