Rattling noise at low speeds on deceleration

Hey peeps I wanted to run this past you guys see what you think. My truck started making an odd rattling noise the other day. When I am decelerating and drop below 20 mph. My truck starts making a noise as if I am in too high of a gear. It has the same feel as if I am lugging and about to stall out from being in too high of a gear... but I am in neutral when this is happening??? my truck will idol perfectly and does not seem to have any problem there. When I accelerate it will vibrate a bit but goes just fine. I have checked my drive train and cannot find any loose ball joints or u joints. I do however know that my front drivers axle has had some play in it for some time now. It almost feels like it’s a gear box issue but everything is riding smooth as can be other than deceleration below 20 mph. Just had the tires rotated and balanced with no change???

 

Could it be a heat shield or the exhaust rattling? Maybe your cat is starting to go bad? I have a similar noise but I'm 99% sure it's my heat shield.

 

After further investigation, it appears the sound is coming from where the drive shaft connects to the transmission. It only rattles when I am braking to stop at a moderate rate. If I decelerate with little breaking effort, there is hardly any rattling. The u joints all appear fine.