DD15 Cylinder Liner/Head/Piston/Rocker ???

Sure you can tear it down yourself , but its not gonna be any cheaper, and will take you longer than a professional wrench...
It is impossible to diagnose any problems without knowing any symptoms you are having. Its like going to the doctor and telling them you dont feel good and asking them if you need a heart transplant...lets start somewhere more simple, what symptoms does your truck have ?

 

Trying to diagnose a noise without hearing it is impossible.
Dd15’s are known for wearing exhaust valves if you don’t keep the overhead adjusted.

 

Can you take a video of these sounds and post it here.. exhaust seeping into cab is an exhaust leak. You should find the leak before it kills you.

 

So watch a YT video on adjusting the overhead and see what you find.

If you pull the overhead first, put a straight edge across the valves to see if one is higher.

Sounds like you have a valve open on startup

 

Time 2. Sounds like some kind of exhaust leak. Like it’s just starting out. OR……. The valves(exhaust side) are to tight and it’s reversing thru the intake air filter, that’s where your getting the sound. It happened on my 3406 E CAT. Hope I explained that correctly to the OP.

 

If you have diagnostic link there is a test that I think is called mechanical compression test. It should let you know if you have a cylinder down.
The hiss on acceleration could be a boost leak,egr pipe or cracked bellows.