On my recent Reatta purchase, I needed to replace struts, brakes, a gasket and fluids etc. The mechanic, who I do trust (not sure why) tells me I need a cat conv. and its covered by exhaust system. He says exh system allegedly needs to be unwelded in a number of spots to remove it. Is this correct?? Be kind, I'm a rookie. Still rumbles in rear, I am going back with it. But... how much rumble and or road noise should I expect? Thanks-- R Russell