Strange Sound When Starting Engine (DT466e)

[Beeb2]

After my recent breakdown in Casper and the awful mechanic I had, I’ve begun to notice a new sound when I start the bus up. Almost like a knocking sound, but it only lasts for a minute or so and then stops. Sometimes it sounds like it stops as soon as the air brakes reach capacity and hiss.

Video with sound:

 

[Malevolence4845]

Exhaust leak or maybe motor mounts?...maybe delayed autoignition..

After my recent breakdown in Casper and the awful mechanic I had, I’ve begun to notice a new sound when I start the bus up. Almost like a knocking sound, but it only lasts for a minute or so and then stops. Sometimes it sounds like it stops as soon as the air brakes reach capacity and hiss.

Video with sound:

I had an old Tractor that would knock until it got warm thanks to a manifold leak, worn mounts could also cause a knock. Your bus is a 2001 right? could be when cold it's not getting enough fuel or enough "glow" from the plugs. get it warm, shut off, drain your air tank and start again, see if it's there while warm with no air just to eliminate that avenue and whatnot. I'm no mechanic but I've messed enough with tractors and I'm leaning towards the fuel or glow issue.

Edit: 1000% sounds like "pinging" from delayed or pre igniting. but try the warm engine no air pressure thing just to be certain

 

[ewo1]

wow...

well I am NOT a mechanic, some here are and I am sure that video will help with the suggestions.

Me being me... I would go old school...grab an old wooden broom handle.. put one end up against your air compressor and the other against your ear...This will help you identify if the sound is coming from the air compressor itself.
I only suggest this because you mention that the sound goes away when the air tank "pisses" when fully charged.

I would also remove the valve cover to see if anything got loose...a visual to to be sure.

could it be a failing injector? IDK !

 

[Beeb2]

I just stopped for lunch after driving all morning (I have no choice but to drive it). I emptied the air and started up again while the engine was still hot. At first I didn’t hear it, but as I’m typing this I think I am starting to hear it again (maybe?). Air tanks are still filling back up. I don’t have a wooden broom handle.

(A few moments later)

Sound went away immediately when the air brakes hissed.

 

[Malevolence4845]

Compressor?

I just stopped for lunch after driving all morning (I have no choice but to drive it). I emptied the air and started up again while the engine was still hot. At first I didn’t hear it, but as I’m typing this I think I am starting to hear it again (maybe?). Air tanks are still filling back up. I don’t have a wooden broom handle.

(A few moments later)

Sound went away immediately when the air brakes hissed.

If having air built up is a common theme it may be your compressor? something worn internally so when its at pressure it removes that slack? It's a little perplexing with the symptoms. I'll ask a buddy of mine who is a heavy equipment mechanic.