I changed out my stock gear oil with Royal Purple GearMax 75-140W on my '06 GT. It took about 2.5 bottles which it should; I filled it until it ran out fill hole. The new seal is solid on diff cover. Now I notice a whine, especially in 4th and fifth @ 2000 rpm. It appears to be more audible when cold, but definately more whine then when stock fluid. Can anyone suggest why this is, or has anyone experienced this problem. This stuff if supposed to quiet gears, but it did just the opposite. I did not add friction modifier because RP says it's not needed. Thanks for any replys or suggestions.