[76TA462]

On my 76 TA I am using the Hotchkis rear sport leaf springs (lowering) and their matching Fox shocks. Over 8 years. Together with the lower front-end coil over suspension and Hotchkis frame connectors things have been great and the ride not bad considering its stiffer. 18-inch wheels with 285 40s on the back. Lately I have noticed a knocking or thumping or deep rattle (hard to explain), not extreme, when I drive over some nasty roads. All good on decent roads even with minor bumps. I have checked everything (rear shackles, leaf spring plates and bushings, front leaf spring connection, axle U-bolt, sway bar connections and etc.). The axle bearings are fairly new and replaced during a Wilwood conversion. There does not seem to be anything wrong visually. When I push down on both rear fenders everything is okay. I removed a jack from the trunk even though I had it down tight. The spare tire is down tight (LOL never needed on for decades, but if I get rid of it I will get a flat). Could this be something to do with a rear shock failing. They are not adjustable and are described as tuned 1.5 street performance matched for the leafs. Thanks.