knocking rear of vehicle

I have recently installed rear shocks on my 2001 buick lesabre custom. Shocks are ac delco with electronic level control. On the road there is an intermittent knocking first on the passenger rear side now on both sides at different times. I have removed and checked the shocks, they seem ok. All is tight under the rear end. Nothing is bouncing around in the trunk. Any thoughts?

Welcome to AF, this was not there before replacing the shocks?

Welcome to AF, this was not there before replacing the shocks?
Thanks for the response "maxwedge." This noise was not there before the new shocks were installed. I did hear a faint sound like something in the trunk on the passenger side for years but didn't think it was anything.

Go back over your installation, something is loose or misaligned.

I agree with the above post.. It is also common for the shock mounts to fail, on these cars its common practice to replace the shock mounts with new socks...

In the 1990s I had a Buick that would make an occasional sort of dry clunk sound, almost a snap sound, usually when stopping or going into reverse. Turned out to be a dry joint (it had a grease fitting). A shot for chassis grease cured the noise (and probably saved the rear suspension from early failure). May not apply to your car - and grease fittings are a thing of the distant past.