Replaced rear axle bushings, still has a knock sometimes...

[Timmmo57]

So, I have been having a knocking noise coming from the passenger rear, which I thought was the shock, but I took that off and checked it and found nothing. I replaced the stock rear axle bushings which looked fine, and used powerflex poly bushings from Woosh. The knocking almost went away about 95% of the time. However, every once in a while, I hear a knock when going over a bump whether it be large or very small bump. It's not all bumps, just about 5% of the time. I checked the rear hatch latch, spare tire/jack, rear seat backs, and spare tire cover. No change. Am i SOL or does anyone have any suggestions of what else to check/do? Thanks very much!