Just instead new headers but there's a light whistling sound

Just installed new headers yesterday, everything fit perfect and doesn't seem to have any leaks. There's a faint whistling sound as I step on the throttle which gets louder with RPM. I'm guessing it could just be from the thinner gauge material and the lack of a heatshield to muffle the sound? The headers are ceramic coated in black. They are PSR UEL Headers which are essentially the same construction as TOMEI UEL headers.