Rubber part #9 in the diagram above was causing extra noise when the spring would compress, noticeable through the cabin with windows up, at low speeds, going up driveways, over speed bumps, etc. Noise was a low frequency rub/groan.
First we sprayed lubricant, took another drive and noted a reduction in noise.
Next, we removed the part altogether and all noise disappeared.
Thanks to Eric from SP who made himself available to help troubleshoot. Much appreciated