referring to fig1 , a prior art noise reduction system for use with an engine driven cooling system is generally designated by the reference numeral 10 . noise reduction system 10 includes fan 12 having a plurality of fan blades 14 extending radially from central hub 16 . central hub 16 is positioned on first side 19 of a conventional radiator 18 and is operatively connected to fan shaft 20 by thermally responsive fan clutch 22 . as is conventional , fan shaft 20 is connected to the crankshaft of an engine which , in turn , drives an alternator that generators electricity . as described , fan 12 is configured such that counterclockwise rotation of fan 12 by fan shaft 20 draws air , generally indicated by lines 26 , axially through the plurality of radiator tubes of radiator 18 , from second side 25 of radiator 18 to first side 19 of radiator 18 . fan clutch 22 and fan 12 are disposed axially between the engine ( not shown ) and first side 19 of radiator 18 . fan clutch 22 may take the form of a viscous fan drive that includes a bimetallic temperature sensing element 24 that senses ambient temperature and causes fan clutch 22 to operate in a disengaged condition when the ambient temperature is below a predetermined temperature and to operate in an engaged position when the ambient temperature is above the predetermined temperature . by way of example , temperature sensing element 24 senses the temperature of the air immediately forward thereof . with fan clutch 22 in a disengaged condition , fan shaft 20 rotates independently of fan 12 . with fan clutch 22 in an engaged condition , fan 12 rotates in unison with fan shaft 20 . in operation , upon actuation of the engine , the crankshaft rotates fan shaft 20 . once the temperature of the ambient air adjacent temperature sensing element 24 exceeds the predetermined temperature , fan clutch 22 moves from the disengaged condition to the engaged condition . as a result , fan 12 rotates in unison with fan shaft 20 thereby drawing air 26 through radiator 18 . thereafter , the air , generally indicated by lines 28 , is urged axially by fan 12 over the engine of the electrical generator . it can be appreciated that ambient air 26 which engages temperature sensing element 24 is preheated as the ambient air 26 passes over the radiator tubes of radiator 18 . as a result , fan clutch 22 is maintained in its engaged position for an extended period of time . once the temperature of the ambient air sensed by temperature sensing element 24 drops below the predetermined temperature , fan clutch 22 returns to the disengaged condition wherein fan shaft 20 rotates independently of fan 12 . referring to fig2 , a noise reduction system for an engine - driven electrical generator set in accordance with the present invention is generally designated by the reference numeral 30 . noise reduction system 30 includes fan 32 having a plurality of blades 34 extending radially from central hub 36 . central hub 36 is positioned on first side 47 of a conventional radiator 44 and is operatively connected to fan shaft 38 by thermally responsive fan clutch 40 . fan shaft 28 is also operatively connected to the crankshaft of an engine ( not shown ) used to drive the stand - by electrical generator . as described , crankshaft fan shaft 38 rotates in counterclockwise direction in response to operation of the engine . fan clutch 40 is preferably a viscous fan drive that includes bimetallic temperature sensing element 42 that senses ambient air temperature at a location immediately adjacent temperature sensing element 42 . temperature sensing element 42 causes fan clutch 40 to operate in a disengaged condition when the ambient air temperature sensed is below a predetermined temperature , and to operate in an engaged condition when the ambient air temperature sensed is above the predetermined temperature . in its engaged condition , fan clutch 40 operatively connects fan 32 with fan shaft 38 such that rotation of fan shaft 38 by the crankshaft of the engine of the engine driven , electrical generator set is translated to fan 32 . it can be appreciated that in its engaged condition , fan clutch 40 may be fully or partially engaged . with fan clutch 40 in the fully engaged condition , fan 32 rotates in unison with the crankshaft of the engine of the engine driven , electrical generator set . in its partially engaged condition , fan clutch 40 allows fan shaft 38 to slip with respect to the crankshaft such that fan 32 rotates at a predetermined speed less than the speed of rotation of the crankshaft . as such , it can be understood that fan clutch 40 causes fan 32 to rotate at a variable speed dependent upon the ambient air temperature sensed by temperature sensing element 42 . with fan clutch 40 in its disengaged condition , fan shaft 38 rotates independent of fan 32 . as described , fan clutch 40 and fan 32 are disposed axially between the engine of the stand - by electrical generator set and first side 47 of radiator 44 . in addition , fan 32 is orientated such that with fan clutch 40 in its engaged condition , fan 32 will rotate in a counterclockwise direction drawing air over the engine of the stand - by electrical generator set . the air , generally indicated by lines 46 , is then urged axially through the radiator tubes of radiator 44 through first side 47 thereof . as best seen in fig2 , a majority of the air , generally indicated by lines 48 , passes through the radiator tubes of radiator 44 and continues to flow axially away from second side 50 of radiator 44 . however , a portion of the air , generally indicated by lines 52 , that is urged by fan 32 through radiator 44 recirculates back through radiator 44 from first side 50 to second side 47 thereof . a portion of the recirculated air , generally indicated by line 54 , is directed back towards temperature sensing element 42 of fan clutch 40 . it has been found that by recirculating a portion of the air which passes through radiator 44 of an engine driven electrical generator set , fan clutch 40 operates in its engaged condition for a shorter period of time . this , in turn , reduces the fan noise generated by fan 32 during operation of the engine driven , electrical generator set . it can be appreciated that the portion 54 of air recirculated back through radiator may be adjusted by incorporating an air duct system for directing the flow of air through the enclosure of the electrical generator or by varying the speed or pressure of the air flowing through radiator 44 . in operation , the engine of the engine driven , electrical generator set is actuated such that the crankshaft rotates in a counterclockwise direction . as heretofore described , this , in turn , rotates fan shaft 38 in a counterclockwise direction . once the temperature of the ambient air adjacent temperature sensing element 42 exceeds the predetermined temperature , fan clutch 40 moves to the engaged condition such that fan 32 rotates in unison with fan shaft 38 in a counterclockwise direction . as a result , ambient air is drawn over the engine of the stand - by electrical generator set . thereafter , air 46 is urged through the radiator tubes of radiator 44 from through side 47 to second side 50 thereof . as heretofore described , a majority of air 48 continues to flow axially away from second side 50 of radiator 44 . however , a portion 52 of air 48 recirculates back through radiator 44 from second side 50 to first side 47 . the portion of air 54 that is recirculated back through radiator 44 flows axially towards temperature sensing element 42 of fan clutch 40 . once the temperature of recirculated air 54 adjacent temperature sensing element 42 drops below the predetermined temperature , fan clutch 40 returns to the disengaged condition . as result , fan shaft 38 rotates independent of fan 32 . it can be appreciated that fan clutch 40 remains in its disengaged condition until such time as the ambient air temperature sensed by temperature sensing element 42 once again exceeds the predetermined temperature wherein the process heretofore described is repeated . it can be appreciated that fan clutch 40 may incorporate a modulating viscous fan drive that does not immediately proceed between the disengaged condition and the engaged condition , but instead begins to engage at a predetermined ambient temperature and gradually increases it engagement with increasing ambient temperature , until fully engaged at an upper ambient temperature limit . various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing and distinctly claiming the subject matter that is regarded as the invention .