Bottom bracket

[Melalvai]

Is it sealed bearing or ball bearings?

Uh...sealed?

I don't think it's normal wear. But ball bearings and their races will wear pretty quickly if they're too loose or too tight, and sometimes they have to be checked periodically because the hardware will loosen up on its own. (Heavy loads will encourage that to happen.)

Heavy loads...yup...

Have you been tightening the cranks on the spindle, or the bottom bracket in the frame?

I haven't been tightening either on a regular basis, but after talking to my bike mechanic friend I will start doing that every 6 mths or so. When I took it in this week, we took it completely out, cleaned and greased things, and put it all back. So we tightened both the cranks and the bottom bracket.

When it clanks, is it just a noise, or is the bottom bracket shifting in the frame or are the cranks loose on the spindle?

Something is shifting because I can feel it as well as hear it.

Could the threads in your frame be stripped or munged?

Definitely possible. Remember the old bracket had to be painstakingly chiseled out of the threads of the frame!