Aweful noise when decelerating above 40mph

[Jwalker1288]

Hey all, I have had this god aweful noise coming from under my truck when decelerating above 40mph, at 75 mph upon light deceleration it sounds like a chainsaw trying to cut metal pipe. The sound does not exist under 40mph and cannot replicate by revving the engine. This has stumped one mechanic who went for a ride with me, I am VERY mechanical myself and cannot find the damn problem, it's driving me crazy! The sound seems to be coming from the front doors forward. I have checked turbo back exhaust connections and removed front drive shaft in an effort to narrow it down but have had no luck at all..

Thank you!

I can make the noise keep happening by feathering the accelerator to different rpm's, higher rpms with higher speeds and vice versa, always between 1250rpm and 2000rpm