Why do Uel headers sound different?
The header piping from cylinders one and three are of a different length than those from two and four. This means that the exhaust gas coming off the engine has to move different lengths, and the sound produced does as well. The sound is unevenly spaced in the exhaust and it exits the car as such.
Are UEL headers loud?
UEL header with the stock exhaust and cat pipe will be louder that stock but otherwise very quiet. There won't be much if any cruising speed drone either. I've dabbled with a few different setups and changing up the catback is where things really start to get loud.