Wadam30

So I just did the 63" spring swap on the rear of my 1987 runner. Everything flexes beautifully and rides just as expected, however, I am experiencing a small vibration when down shifting. I've been under there countless times to make sure everything is tight, lined up properly, measured correctly etc. The only thing that I can think is I have the inside pretty much gutted so there is not much weight (not that the interior trim adds that much weight) and could be the tires chattering. Any ideas? Your guys' advise is always appreciated. Thanks!