Engine knock only in park or neutral?

I've heard this quiet tapping for about 10,000 miles now. Just changed my oil/filter and fuel filter yesterday and now it is noticeably louder. I can only hear the noise when its in park or neutral, the moment I put it into drive it goes away. I have no check engine light and the truck has been running fine. I've got about 90,000 miles on the timing belt so I'm going to replace that this weekend but I can't see that solving the issue. Does anyone have any ideas?

Here is a video of the knock. Volume at max you can hear it especially towards the end, its the deeper tapping/knocking sound.

https://youtube.com/shorts/itD53BcKS4M?feature=share

 

It's probably not a knock if you don't have a knock sensor code. But I hear what you're saying.

It sounds like a cracked flex plate to me. That's one of many topics covered in the 'shit you should know about your 1st gen' megathread.

Search that thread for the word "flex". Follow the two links in that bullet point to compare. There's a recent thread with similar videos to yours on here, similar sounds. It might just save your ass.

Note: It doesn't always sound like the 2nd thread with videos.

Also, if you're 2WD, that would be good info to know.

 

Any noise from under the truck ?

 

I just crawled under the truck right now to see if I could hear it from around the flex plate and no, it sounds like its coming more from the front of the engine. Like above the oil pan and forwards.

 

Get an automotive stethoscope or put your ear to a long screwdriver.

I'd wager if you're flex plate isn't the source for your tick it's exhaust manifold.

 

I'm not sure if you heard the right sound, I'm familiar with the exhaust leak problem but I'm talking about the duller, less-frequent tapping sound. You can hear it clearly at around 11 seconds in the video.

 

Engine mount? The only reason I say that is b/c it disappears while in drive.

Any codes currently registered? Don't trust the check engine light, they burn out and sometimes POs will remove the bulb.

Does it change with RPM while in P or N? Just trying to understand if it stops when the accessory drive is under tension.

Is it louder in front of the engine, or one side? I guess at this point, 1st and foremost, knowing the timing belt should be changed every 90k-100k, which I assume you've done ... I'd probably be popping off the serpentine belt, wiggling pulleys, checking timing belt pulleys. But given so many people don't understand having the timing belt snap can brick your whole engine, I'll toss it out there.