The motor is old, the blades a bit out of whack, and most of the noise is really coupled to the cabinet by the decayed and ineffective rubber isolation bushings on the three-point mounting plate.
In this parsimonious approach the two rear support plate studs are coaxed slightly to fit a 60 x 60 mm 10 CFM Fulltech unit {Jameco 213867}, while on the other side the fan’s ground hole is supported by a brass strap that needs no fastening. Though not mechanically isolated, the substitute method is inherently quiet and efficient.
And if you are motivated to search for the parts, nothing prevents you from replacing the original fan and suitable gaskets for the original mounting plate.
