Popping sound from Cat?

Vehicle is a '98 K2500 with 5.7L (350). I just finished up replacing the intake manifold gasket. Upon initial startup, I get a loud metalic popping sound. Almost like something was left in the vicinity of the belt. Not
rythmic, though. It was one of the first things I heard the instant the engine caught and ran. I shut it down and looked at the belt and pulleys for any sign of anything caught or somehow in the way. Didn't find or see anything. Checked over the connections and all seem OK.
Engine is also misfiring and the Service Engine Soon light is on and constant. I figure that this one is caused by moving the spark plug wires and getting a misfire from this.
Could the popping sound be the cat trying to burn raw gas from the misfire? This truck has 2 cats. To me it would seem to need some time for the cat to heat up before this could happen. The popping sound, more like a banging sound, starts as soon as the truck is running. I haven't run it for long, just in case. :-)
Some online sources say a vacuum leak could cause this. Other than the brake booster line, what other vacuum lines should I look for? I don't remember unhooking any, but my clumsy fingers and arms seem to find places under the hood I didn't know existed. :-0 I might have accidentally knocked something off. I'm going over it with a fine tooth comb to check, but will use any and all ideas and suggestions.
If you need any more info, please let me know.
Any help you wish to offer is greatly appreciated. Thanks.
Bill
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Figured out the popping noise, In my tiredness from working on it all day, I messed up the spark plug wiring. Straightened that out and no more popping.
Still have the SEL. Code that I get is P1345. According to my scanner the CMP/CKP is out. It reads 22 degrees on the camshaft. I think I'm going to retime it as to set the distributor I need to turn it clockwise and the wires are already against the bracket. I think it is one tooth off. It does start hard, cleaning the battery terminals didn't change that.
Appreciate any suggestions.
Bill

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