TDG MAFIA MEMBER #77
Join Date: Jul 2006
Thanked 11 Times in 10 Posts
Nothing to worry about on either truck. Your truck has an Exhaust Back Pressure Valve (EBPV) in the plumbing on the turbo. At low temps and low RPM's it will close partially to help warm the motor up quicker. The hissing sound you are hearing is just part of the deal.
1999.5 PSD, 4x4, Auto trans, 6.0 Trans cooler, ZooDad Mod, ISSPRO Trans - boost - EGT gauges, Wicked Wheel, 5inch Stainless tip, 315 75 17 BFG AT's, ProComp 9000's at the corners, Fumatomo Valve, Pooned tank, DP Tuner F5 w/ 80 tow, 80 econo, 120 race and permagrin!