B&B Heat Exchanger (heater box) started rattling!
 

All of the sudden there is a very loud rattle from my engine. I thought it might be the tins as one seemed to be not tight. The noise is very prevent ant on a cold stares, as the engine vibrates a little more. Once its warmed up the rattle goes away at idle, but if you bog the motor down you can hear it clear as day. I crawled under the car and the passenger side heater box is the cause. It moves a lot more than the drivers side (both move a little), and putting your hand on it stops the rattle. They are B&B headers on a 964 motors.

So whats the cure?

Spot weld them in a couple of places to the headers