The LBZ trucks remain pretty quiet with all 4" systems. If you want it as quiet as possible though, i would go with the Diamond Eye exhaust with Quiet Tone front pipe. This system uses a resonator in the front pipe as well as a large muffler to keep the noise level minimal. The only problem is, they are only available in aluminized steel. Your other option would be to get an MBRP kit and see if that gets you what are you looking for, if not, you can always add a resonator to the front-pipe. Here is a link to the DE Quiet tone kit as well as the 4" T409SS MBRP kit. Feel free to contact me if you have any questions.
DE Quiet Tone Exhaust
MBRP 4" T409 SS Exhaust
DE Quiet Tone Exhaust
MBRP 4" T409 SS Exhaust
