If you mean the small end bearing, you'll hear intermittent or continuous tapping noises or if you've got piston and/or bore wear it'll make a high pitched rapid tapping/rattling noise (piston slap) when running under little load or just at the point of giving it some beans, a rebore to next oversize plus oversize piston is the only option here. If its the small end you may have had lubrication failure which you'll need to find out why.