I am experiencing a loud knocking noise from my front RHS wheel. It's intermitten and happens while turning. Sounds like gun fire. Inspected under both wheel wells, cannot see anything obvious. RHS wheel can be turned by hand but seems to be grinding. Any ideas as to what may be the cause?

It's a '97 XK8 with 70K on the clock.

 

About the only thing I can think of that would make a grinding sound is a bad wheel bearing, but read my disclaimer below. I guess it could be a brake issue, too.