'97 4.3L CPI Rattle at Low RPMs

Have a '97 4.3L CPI that is rattling at idle or low rpms. It appeared to be a bad pulley (alternator or tensioner) however, temporarily removed serpentine belt an trouble continues.

Symptoms:
1. Rattle or knock at idle or low rpms only
2. When operating the throttle from the engine compartment, can "feel" the rattle in the linkage until rpms increase.
3. Rattle will increase when incurring electrical load (ie. continue to move electric seat to back position AFTER seat has reached the end of travel) - only notice a very slight dip, less than 1VDC from 14VDC on gauge.
4. Rattle will increase when in Park and turn steering wheel either left or right.

First thing comes to mine is, if you removed the serpentine belt and the noise continued. I would check your Harmonic balancer and pulley. There is 4 bolts. The bolt in the center is for the Harmonice Balancer, and the 3 on the outside is for the Pulley. If that checks OK. Then check your Fly wheel. You mite have some loose bolts. You'll need to remove the dust cover on the bell housing and turn the motor by hand to get every bolt on the fly wheel.

Check your exhaust and catalyst. Mine did the same thing like your rig and it turned out to be a U-bolt that turned loose under the truck. It would rattle and squeak at idle with the truck in gear and when you turned the wheels sharply. Localizing it under the truck, took my deep socket set and torque wrench under the truck and tightened up the offending U-bolt on the exhaust. A miracle I did not loose the whole works since it was so loose, but it was just jangling and rattling around like there was no tomorrow.

Check your exhaust and catalyst. Mine did the same thing like your rig and it turned out to be a U-bolt that turned loose under the truck. It would rattle and squeak at idle with the truck in gear and when you turned the wheels sharply. Localizing it under the truck, took my deep socket set and torque wrench under the truck and tightened up the offending U-bolt on the exhaust. A miracle I did not loose the whole works since it was so loose, but it was just jangling and rattling around like there was no tomorrow.

Yea, this does sound like an exhaust problem or even a motor mount letting loose.

Check the exhaust and all motor mounts.