1. A heat exchanger comprising:a bundle of tubes inserted into a housing, wherein exhaust gas flows through the tubes; a tube plate fitted onto an end of the bundle of tubes;
a diffuser having a first end joined to the tube plate and having a round shaped portion at a second end opposite the first end;
an elastic element supporting the diffuser within the housing at the round shaped portion, the elastic element permitting differences in thermal expansion between the bundle of tubes and the housing;
a coolant duct arranged between the tubes;
a grid-like securing structure joined to the bundle of tubes; and
at least one metallic spring attached to the bundle of tubes, spring force of the at least one metallic spring being directed against the housing in order to reduce the transmission of vibrations wherein the bundle of tubes and the grid-like securing structure are joined together as a stainless steel soldered structure and the at least one metallic spring is attached to the bundle of tubes after the soldering.