Banging noise on spin cycle

My washer has started making a banging noise in the spin cycle. I have opened the lid and watched it and the agitator seems to jerk to a complete stop and or wants to go back to the wash/agitate cycle for a second then starts to spin again only to repeat the stoping/banging throughout the spin cycle. There are no broken springs on the tub. The belt seems to be a bit loose as I could easily remove it by hand. Could a slipping belt be causing this problem? Is the moter suppose to float (be loose enough to move by hand) where it is connected to the two bushings through the bottom of the washer? What do I need to replace before some real damage occures.
thanks

Additional information…now the washer will not spin at all…water drains out and agitator stays in the wash cycle. No spin