<E36> annoying centre subframe rattle - help !

[Dr Chris Slinger <slinger@xxxxxxxxxxxxxxx>]

My E36 325 TD SE has a rattle under the car from somewhere located below
the automatic gear selector.  It rattles whenever I start or stop the
engine, or go over even minor road bumps or potholes and is getting
progressively worse.  On looking under the car, the rattle seems to be
associated with the bracket that is bolted to the proposhaft tunnel, the
bracket supporting the central section of the exhaust (via 2 thick rubber
washers) but also (perhaps) a propshaft mount.  The sturdy aluminium
bracket is bolted to the underside of the car using 4 bolts (13 mm heads),
2 on each side of the prop shaft tunnel.  If I pull on the bracket hard
(or the exhaust in that region, or pull down on the propshaft), I can make
something akin to the rattling sound.  I've checked the bracket's bolts,
and they all seem tight.

Any ideas what is causing the rattle ?  Why is it getting worse ?  How do
I stop it ???  Very annoying.

I'm a novice mechanic, BTW, so please no replies along the lines of "first
remove the automatic gearbox.." :-)

Any help appreciated !

- -chris

------------------------------