I have a 4" turbo back with a muffler and it drones in the cab above 75 (tells me when I am excessively speeding). Otherwise it only sounds loud outside the truck but not inside. I would say leave it on unless you don't like listening to your passengers.
00 F350 CC LB 4x4 auto. Nitto Terra 285 75 r16 E, Dynatrac free spin hubs, ccv, rancho stabilizer, centramatics, upgraded GPR, DB starter, 2.0 ga pos cable, matching 5th rim, 6637, 4" SS magnaflow, CPR, Scan Gauge, Mag Hytech.
USN VBSS, Burn sink or take a-prize.