My Dynaco st35 noisier than i recall?

...constant hum through the fostex drivers,it's constant,equal through both speakers and fixed(as in the pitch does not vary(i think some kind of earthing/mains issue.My question is this,i run the nad 3020 as pre and i was wondering.....the st35 in it's original state would have had a simple mains lead with no earth but when i bought this unit that was already removed and fitted with a very thick(almost 2 metre long) "Audiophile Grade" ;D cable which i now see is connected with an earth.....could this abnormally long cable cause issue?...can i remove the earth?....it did not have one originally i think?The mains plug is something called a PROP.....Nasa grade with solid gold pins  ;D