washer tub spinning off center

i have this frigidair mlce52rcs1 stackable washer and dryer. recently the tub has started spinning off center. it’s a little off center leaning to the left when nothing is in the tub. if i pull it back it gets close to center again but does not stay there. it seems to was ok but does make a little sound that i believe is associated to the issue. i can pull it back to center while it is washing and that sound will go away. however when it spins its like the load is out of balance and the tub shakes quite a bit. it does not go off line for being unbalanced. is there a service manual available and does the washer top come off to check it out. all the links i found for the manual do not work.