Well as part of the 6 monthly big clean i scrubbed the circulation and main tank pumps. When i put the main tank pump back on i got a rattle, it's been driving me nuts for days. Anyhow, i decided to re-strip the main pump down again as something just felt "off" and as i was doing it, I noticed a little black washer in the sump. Must have fallen out on the initial strip down.
Anyhow, popped the washer into the impeller chamber, reassembled and voila, rattle gone! Everything is now back running lovely and quietly. Learn something new every day in this hobby!
Did a water change and tank clean tonight too, so I will try to post some new updated pics this weekend.