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Alright, this is my first post here so if I'm doing anything wrong, let me know.

2000 Mustang V6 with stock 4-speed automatic transmission.

The short version of the issue is that I'm hearing a metallic knocking sound coming from the front half of my car, there is no check engine light, and there are no error codes on the ecu.

It only happens when I have let the car warm up for 10-20 minutes, or I've driven a couple of miles, and it only happens when the car is in gear.
Once the car is at operating temps, I can rev the engine in neutral up to 2500k+ without any odd sounds (other than leaks from old gaskets I need to replace, we'll get to that soon though) but as soon as I put it in any of the drive gears the sound shows up and gets louder when revving.
I originally thought it was a spun bearing, or something in the valve train, but I inspected everything without finding the cause. The oil pressure stays the same and there is no noise when the engine is under load, so I am pretty confident that it isn't an engine issue. The idle speeds go down from 1000 rpms to about 500 when I drop it into gear.

I have already taken off the intake manifold, both valve covers, checked all 12 rocker arms visually, checked the plugs and wires. I have a few ideas, but I want some help before i start ripping more off of my car.

This car is my daily, so any and all suggestions for what to look for would be appreciated.
If you need any more info, please let me know and I'll get back to you asap.

Thanks, Josiah.
 

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Hmmmmm………….One thing comes to my mind (SWAG)….check the harmonic balancer....it may be starting to fail causing the pulley to lightly contact the block..... they are not always consistent deviation and when different loads are applied, the effects can vary.
 

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Hmmmmm………….One thing comes to my mind (SWAG)….check the harmonic balancer....it may be starting to fail causing the pulley to lightly contact the block..... they are not always consistent deviation and when different loads are applied, the effects can vary.
I actually just replaced the balancer about 6 months ago with a brand new part straight from Ford, so I highly doubt it's that. That feels more like sitting on an old dryer filled with tennis balls 😂
I'm thinking it could be the flexplate is damaged/not installed properly anymore.
 

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I just had a similar incident with a 6 cylinder PU. the noise got so bad you'd want to shut off the truck. Like you, no lights and the engine ran great. It turned out that the catalyst had broken loose inside the head pipe and was banging away. up on the lift new pipes all the way back and fixed the trans mount while it was up there and an oil change. got away for around $500 now you can't here the truck run. Don't know if the mustang of your vintage has the cat on one head pipe then a second cat further back or not. just something to think about
 

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I actually just replaced the balancer about 6 months ago with a brand new part straight from Ford, so I highly doubt it's that. That feels more like sitting on an old dryer filled with tennis balls 😂
I'm thinking it could be the flexplate is damaged/not installed properly anymore.
Could be but it might also be an oil pump failing or related issue.
 
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