My wife said the noise started just as she turned into our neighborhood this morning. Anyway, I'm not getting a CEL, I even went on to scan it with my cheap scanner to see if there were any stored codes; nadda!
The noise sounds like it's coming from deep within the engine close to the firewall. Both the engine oil and trans fluid are good.

Here are the details of my runner...
98 w/3.4 auto
175k
oil changed regularly
recently had a freeze plug replace.

Here are my observations so far...
The knock happens when the truck is idle in park and in neutral.
Whatever it is makes my engine sound like it's missing, even at idle.
No codes.

Any ideas or suggestions are appreciated..
-e

 

Whats your timing belt history?

 

It's due. I think I've been on this timing belt for the last 50k.
Do you think the belt "jumped a tooth"?

Forgot to post this earlier.. The knock is not consistent. It can go away for up to 30 seconds and come back.

Thanks for the response..
-e

 

I think it may be that... I dont know for sure. Mine is due and I have the same issue. I read somewhere that it may be that...(I dont know where)

 

The timing belt should be fine with only 50K miles. The new change interval is 90K miles for those.

 

sounds like it could be a broken flexplate, a knock in an engine is not a good thing. Rod, main or wristpin failure, (worst case senario). The flexplate would be the best

 

Check your crank pulley and verify ignition advance with a timing light.