had to tow the 72 home today

[jd4300fel]

Took my daughter out for an icecream, on the way home cruzin down the highway, I was only doing 50 or so. I asked my daughter if the truck was sounding louder than normal and she said yes. It sound like one of the mufflers was falling off or loose. I kept my eyes on the gauges and everything was where they are suppose to be. We went another nine miles and it was stayin about the same going through town it started to make a horrible noise like someone was rattling a coffe can with loose bolts in it.
This truck has always blew blue smoke at startup and then it clears up. A week or so ago I was low on oil I added a qrt and everything seemed to be fine. I am hoping to bull the valve covers off today or early this week, I am not sure what I will find. This truck was currently just used to go for a quick drive it's not my daily driver so that is a good point.
the truck has a 400 big block.