They're poly, right? Whiteline definitely don't do that. But I haven't heard anyone complain of Energy diff bushings doing that. I would be tempted to take it back to the shop for another look. If they say that's normal, take it to a competent shop for a second opinion.
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2011 370Z 6MT Sport Gun Metallic | ARC | CJM | Ecutek | FI | Fujimura | R2C | SPL | Stillen | TWM | Z1 | ZSpeed | |