Rattle noise from engine?

Anyone have any idea why we would suddenly have a rattle from the engine - only at low RPM (1500-2500) and in the top gear (auto transmission)?? Very unnerving but no loss of power (that RPM and gear doesnt produce much anyway?/). Thanks for any help!

Any idea of "where" in the engine it's coming from? Does it sound like a metal on metal kind of thing? Any other descriptors you can think of?

I cant narrow down the location - only sounds when in the high gear so cant get it to replicate at idle. It almost sounds like a very small marble inside a baby rattle - but banging around fast if that makes any sense?

Low RPM high gear, this might actually be "pinging". just for grins next fill up try premium, unless you already use the higher octane. Just to rule out engine knock. But the scenario you gave sure lends to this being the problem.
A bad tank of gas can also do it.
Let us know.

It could also be the heat shield on the exhaust, we had a similar problem on my wife's Forester when the heat shield broke a weld on one side - it would only rattle when the engine revs hit a certain range in the right gear.

If it is the heat sheild as he mentioned then a quick but TEMPORARY way to validate this is to stuff a wad of steel wool in the gap between the sheild and exhaust pipe, IF you can get to it.
I did this on a vehicle I owned and it actually lasted over a year!
Good luck

I own a 2006 forester it has a rattle also but is in the exhaust.It happens only when the car is cold and about 1500 rpm.Of course when i brought it in for service the tech couldn't find anything.I suspect it is the heat shield on the catalytic converter

We acutally removed the heat shield from our '02 cause it was so loud. A mechanic I know said it wouldn't be a problem.