Should a catalytic converter need replacing at 44,000 miles?
on 2000 Buick LeSabre

The exhaust sounds like metal rattling when starting and when the gas petal is pushed down. Is driving too little (3000 miles or less a year)cause for this to happen?

How can I be sure that a NEW CC is being installed?

Asked by for the 2000 Buick LeSabre
Could be loose heat shields. Verify , by asking for the old part back , and actually asking them to show you the new one on the car. OR find one shop with good references , that you can trust , and stick with them.