Noisy pistons aren't much of a concern, as even a few thousandths too much clearance can get pretty loud without doing any damage. Usually, though, loose pistons make more noise during warm-up, before they heat-expand to closer tolerances. As long as the rings are getting a good seal, there won't be much oil consumption, even with a very sloppy piston skirt fit. Normal piston-to-cylinder clearance will be in the .0015" to .003" range (one or two strands of hair) and they start getting noisy at around .005".
How's the oil pressure? if you're experiencing a noticeable drop in oil pressure at about the time the noise starts, you're dealing with loose rod bearings, not piston fit troubles. That situation will worsen as the oil heats up and thins out. An "owner-rebuild" without doing some precision measuring and corrective machining can be a very short-life situation. It's also possible to put one or more pistons in the engine backwards, causing the offset piston pin to face the wrong way. That creates some rattling noises almost like a Diesel, but it's obvious from the first startup. I walked into a friend's shop one day just as his engine mechanic fired up a fresh rebuild, and it sounded like a Cummins engine instead of a stovebolt. When I commented that all the pistons had to be in backwards, the guy said "No way!" We ended up with a $100.00 bet over it. He dropped the oil pan back off to prove me wrong. I won!
Jerry
