1990 525i with 240k miles - car/engine is loud

It look slike I am getting my transmission swapped out and while they are doing it, I might fix whatever is wrong with the exhaust since it's so loud.
A similar car to mine pulle dup beside me the other day and sounded the same way so it might be common enough in these carrs to diagnose over the forum.
The manifolds have little corroded holes at where it bolts into the block.
Inside the car when it's running, it sounds like you're inside the muffler, almost too loud to talk over.
When it's pulling in the driveway, I can hear the car from inside the house as it's coming down the driveway. When you lif the hood, it' s not louder than any other car. Behind the car or beside it with the hood closed, it's a low muflled roar.
The junk yard I am buying the tranny from has lots of used BMWs so I might get them to ship whatever I need for this as well as the used tranny.
Any ideas or what to look for?
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