Rattling noise/slight vibration accelerating under 1750rpm

[maxmileage]

Crazy hard to figure out. After I cross 1750 on the rpm gauge it goes away. Hear/Feel it most in 2nd and 3rd. strange that it goes away on a dime and no other issues. Had most of the heat shields ripped out when I had the rusted out exhaust replaced. Still there. Been there since I bought it a few months ago. Any ideas? all u joints check good and everything is tight. Changed all fluids properly. Haven't gotten it up off the ground to see if it does this under load yet. Hopefully this weekend.

[Chris.m]

Go under the truck and start beating the exhaust with a hammer. If there is a strange intermittent noise caused by the exhaust, you might hear it.

It worked for me.

[Slumpert]

checked all the motor mounts?

[maxmileage]

Don,t think its the mounts as its coming from the rear of the vehicle.

[qx4dude]

Check to see if the Exhaust flange right over the rear axel is rusted out. I just had to this on mine.

[Slumpert]

Well being from the rear and alters with engine speed I would also think it is a exhaust item.. Even muffler. Might be putting more exhaust out as the engine is more loaded under 2/3 gears..

Taps from a rubber mallet on the exaust parts might help.

While under there, be on the lookout for the previous owner doing something silly like using coat hangers to hold up the pipes.. check each connection