Here's the critical final step in a new gear install, break in and heat cycling.
If this is not done, you will have nothing BUT trouble from a brand new set of gears. Drive the car moderately for 45-60 minutes and park the car for 3-4 hours. Do this 5-10 times. This will allow for a solid wear pattern to set in and will also finish hardening the new gears before you jump on the gas hardcore. I would drive the car enough for this to happen before heading back to the installer.
If the new gears are still making a lot of noise once a wear pattern has set in, then there is definitely a problem. It could be a simple as backlash not being properly measured.
I agree 100% with Blue Streak.
Quite frankly I am tired of hearing about "certain brands of gears are worse....". Frankly, it doesn't matter one bit as long as the new gears are installed properly meaning pinion depth and backlash are in spec.
Before I did gears on mine, I too asked on here and everyone that responded said Motive brand were the worse, blah blah blah....Guess what, I bought Motive brand installed them myself, set the depth and backlash, checked the paddle marks, HEAT CYCLED the gears just as Blue Streak said and I have no noise whatsoever.
Installation and breakin are key, period. :bigthumbsup