[3.4 grape of wrath]

I installed a set of the Founders f-body rear coil overs awhile back along with a Strange 12 bolt. I understand the rear creates more noise then stock, so some of the noise might be from that. The coil overs do not have any insulators at all and I thought most of the noise is being transmitted from them. The noise isn't horrible but seems to get worse with more rpm's. I would describe it as a drive line vibration. Has anyone installed rear coil overs with similar results? Any fixes?