Banging Noise in 99 Silv

I have a loud banging noise in the front end of my 99 5.3L LS with 135k miles. The noise has no rhythm, happens at idle when engine is revved up or engine is facing uphill and while driving. Sounds like a not being thrown against the wall of something. It hasn't effected my milage at all... still get 19+ mpg. I had my 100k mile tranny service and mechanic said it looked fine to him with no metal in the trans. I also replaced the water pump and fan clutch. Any ideas?:screwy:

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Any thoughts???? Anyone???

Anything hitting the fan? Blades OK?

We looked at that, but the noise is so intermittent it can't be something connected to something. Does that make sense? It sounds just like a nut or bolt being thrown against the side of a metal compartment when something picks it up and throws it.

Does it do it while idling in Park and revving the engine? With the hood up and having somebody rev it while standing nearby, might be easier to isolate where it's coming from. Wear safety goggles JIK it is something being thrown.

I have had alternator bearings go bad and make the same noise you are describing. Can you get a mechanics stethescope and listen to the alternator bearings while the engine is running? Sometimes just a long screwdriver will work, but the stethescope is much more sensitive.

I had a noise that was driving me crazy...it was a sound like a metal plate rattling. I removed the bottom of the dash to mess with my turn switch wiring the found a metal plate with four nuts that one nut was missing and the other three were very loose. I tightened them up and no more rattle.

spun rod bearing?

Thanks for the suggestions, guys. I like the alternator idea more than the spun bearing, but the sounds seems low in the engine/transmission area. Grrrrrr.

Might be a broken motor mount. You gun the engine and it lifts up and the fan might knock something. Then you get out to check and nothing is there. Put on the emergency brake and have someone in the cab hold the brake firmly and give it some gas. Stand on the side of the truck with the hood open and see if you can see the engine move.

Thanks, I'll check that out too.

spun rod bearing?

This gets my vote too. Mine made a tapping/knocking sound at idle, and it got louder the higher you revved it.

Might want to check the oil for metal shavings.