Thank you very much for your reply.
Does the fact that thhe whirring seems to stop after the car has warmed up tell you anything? My guess is that the lower heat shield is just touching the cat, and that when it gets warm enough, the connectors expand so it no longer touches. Thats a wild stab in the dark though.
I have meant to reply for some time though, but not had time.
I havnt had time to poke around under the car. Should I expect bolts holding the heat shield on, or is it welded. (Would I have to cut it?)
Is it safe to just remove it? I have heard of people setting patches of grass on fire with old catalytic converter without heat shields. What is your risk asessment?
Thanks for all the help,