Another Rattle Noise

Hey folks, have a metallic rattling noise that occurs intermittently at idle or very slight gas or brake application and only at low speed or stand still though not guaranteed to always occur. I can slowly come to a stop and it won't happen, it never happens while on a positive (facing uphill) gradient, and sometimes on a downhill. Once It starts it ALWAYS will stop when I put the truck in neutral.

Truck is heavily modified, basically everything in the suspension, CV axles, full Underbody skid plates. Transmission and motor are OEM.

Because of the connection to idle and how it always goes away when shifting in neutral it tells me that it's either drive train related or induced by drivetrain.

I've been wondering if there is something lose on the under body skid plates so my next triage was going to be to take everything off and see if it goes away.

The only other thing I could think of was something like failing idler pulley bearing.

Thoughts?

 

I had a line come out of it's clamp under the hood that had similar symptoms. Think it was a fuel line coming out of the high pressure pump. It only rattled against the clamp when warm and idling in gear, when the engine speed is lowest. Just happened to be the right frequency.

 

Geez man, it could be just about anything!