This is kind of far out, but this board is so good, I'll give it a try. My gandson's Volvo has a "rattely" sound that comes as follows: With my head down between the exhaust manifold and the fender, there is a loud, tinny, vibrating noise that comes either from the transmission (automatic) or the exhaust system. It occurs when the engine is reved up to about 2500 rpm; it isn't there below that speed and disappears above that speed. Is it possible that there is something loose in the catalytic converter? I don't know what there would be in the transmission that would cause that noise.
Anybody else experience such a noise?

This is a very common noise for 240s as they get to be "of a certain age." It is almost always one of the exhaust heat shields on the front pipe or around the cat converter itself. With the engine cool you should be able to bang gently on the heat shields with a mallet to see which is the offending one. The best course of action is just to remove it. They're not necessary at all, but you might want to be careful not to park in any fields of long, dry grass (that's about the only time I can think of where the heat shields might be of some benefit). You can remove them by cutting them or prying them off in some fashion. They're not that hard to rip off once you get them started, but be careful not to bang on the exhaust system too hard because you might open up some leaks elsewhere.

There's also an attachment bracket from the tranny or from the crossmember there, holding the 1st exhaust pipe. That's the pipe located between the manifold and the cat. I've had them rattle some, especially if that pipe was replaced.

Reason:
Replacement pipes usually don't have the bolt hole for that bracket in the right spot. So the tech leaves it unattached, and the bracket vibrates against the pipe. Last one we had done, the tech cut off the bracket. No rattle. Fine by me.

I'll check out your suggestions when I can corral the car. Might be in a week or so. I'll let you know what I find.

Al