I wonder if anyone has any suggestions with this little problem. On the day that GM declared itself bankrupt (ie yesterday) my Miggy has delveloped a slight light rattle from the bottom of the engine somewhere which sounds like a loose heatshield. However the odd thing is that if I swich off the Climate control it stops. Switch on the climate control and it starts again. It seems to come from the bottom of the engine somewhere on the offside and cannot be heard inside the car only when you get out and listen. A/C is working perfectly with nice cool air. Anybody got any suggestions on this one?  Many thanks in advance.

IMO if its a V6 may be the heat shield around the down pipe. They are probe to becoming loose. Engine is under slightly different load with A/C on so may be causing rattle. Can you update your profile please so we know which engline/miodel you have please. Would help with replies.  :y

JezInBrum many thanks for the reply car is a 1998 Omega Elite 3 litre this info appears to have disappeared from my profile and has now been corrected. Just need to work out how to get access. 

Strangely enough, noticed mind had too. Done via the UserCP tab at the top of the screen, then go to edit profile.
As for your problem, try reaching under the car when running and using a very thick piece of rag to (to avoid burning yourself), briefly hold the shield to see if rattle goes of subsides.