how do i fix my Hotpoint Aquarius Extra WD64?

When my machine goes to spin throughout its cycle the drum makes a loud knocking sound. I have investigated the problem and thought it was possibly the belt not being seated correctly, re adjusted and tested, sounded ok, put a full load in the drum and as soon as initial kick start to drum, knocking was heard.
I suspect the pistons that stabilize the drum, but also considering the bearings.
Need to know if either or can be fixed easily and cost effective. WD64 is 8 years old but is in good condotion.