Watched video on coupler repair. Put coupler in with socket. Looked seated level to edge. Put back together. Started in spin. Loud squealy sound. Now machine just hums. Took apart again and could see wear on rubber part between coupler halves. Strange. Original coupler was found broke. Any help would be appreciated. Need to know if I should have seated beyond flush or what? What is hum indicative of? Just trying to save a dime.