XHD Leaf Springs

Last fall, I replaced the factory leaf springs on my 65 Barracuda with a set of MoPar HXD springs - which made the right side of the car sit about one and one-half inches higher than the left. This was somewhat distressing, but assuming that the new springs would "sag" in a few weeks (and balance out), I drove the car. Initially, I noticed a bit of a "grinding" sound from the rear end - but it soon disappeared.

But the springs never did sag (which I assume is a good thing), and I took a look at various Web blogs to see if anybody else was experiencing the same situation. I found some information which led me to believe that the right spring is actually quite different from the left - and is perhaps suited for serious oval racing (?).....

Anyway, to level the car, last weekend I installed another new XHD right spring on the left side. Voila - the car is level, looks good with the extra "lift".... and I'd be a happy camper except for the god-awful noise coming from the rear end.

I'm not exactly sure how to describe this noise, but it's a phenomenal (and quite loud) harmonic whistling type of sound. It starts as the car begans to move, and stops when the wheels stop moving.

Any ideas?