I was hearing a hammering noise this weekend, the washer spun fine but would hammer loudly at the end of the spin cycle. I could spin the inner tub by hand with the washer turned off and it was clunking at 180 deg every time. I decided to remove the agitator to see if something had caught in the bottom of the drum and found nothing. I spun it by hand again saw the drum slipping on the drive block. I re-installed the agitator and found that the bolt had loosened and allowed the drum to jump the drive block. Replaced the agitator bolt and the rubber washer under the head and problem solved for just a few bucks.
It sounds like a different problem than the OP but this was close enough to my problem to get me to read and it may help someone out with the same issue.