The problem is the TRD exhaust. The USDM TRD exhaust with barrel muffler is known to be quite loud and raspy when you get headers/remove cats
There are other aftermarket exhausts offered with quad tips. Even if the bumper is cut for quad tips, you can also opt for dual tip exhausts.
- The cut-out for quad tips simply enlarges the original dual tip factory bumper clearance. Dual tip exhausts will fit just fine under the bumper (albeit the tips won't fill up all of the exhaust cutout area, leaving some empty space). You don't need any bodywork for dual tip exhausts unless the empty space bothers you.
Blitz, Fujitsubo, HKS, Greddy, and others offer quad tip versions if you are so inclined. Many more options abound if you are willing to consider dual tip