I have a 1990 Dakota with a 3.9L V6, Automatic Tranny,
2 wheel drive extended cab. I have owned this thing since '94. It has always had a pretty severe sounding resonating vibration at around 70mph. It seems to originate from the engine compartment and is worse when after reaching 70+ you let off the accelerator. I have spent 14 years trying to find the origin of this noise and have yet to find it. It doesn't seem to effect the performance or have any adverse effects on anything, it runs and drives well. I was hoping someone else has had this very problem and can help me figure out what this is.

I had something similar at 65 to 70 mph, 1900 to 2000 rpm, found it was the dual exhausts resonating through the cab. Fitted a new back muffler, almost silent.

2002, 4X4, 4,7, 110K.