If the other suggested stuff does not work listen with a piece of broom stick or a mechanics stethoscope to see if you can locate where the noise is coming from.

The Vacuum Pump having issues can make noise.

Removing the small steel oil pan and looking in the bottom for metal fragments might also tell you if something is destroyed.

When I first got my Car the engine would shake and the Air Filter Housing would pound on the intake manifold. Some where there is thread that tells you to put a piece of 3/4" or 1" heater hose between the manifold and Air Filter Housing.
The noise was bad and sounded like something was going to break off.

The same as above but caused by a broken Air Filter Bracket.

__________________
84 300D, 82 Volvo 244Gl Diesel

Well, just as long as the canola is in the fuel. Diesel Purge is the same, the engine runs quiet while you've got it running through and people think it's fixed something but then the noise returns more often than not. Both are quieter because they burn easy, I guess.

The first time I dumped some old (but unused) cooking oil in my tank I thought the engine died when I was idling through a parking lot it was so quiet.

-Rog

I think the flame front is more gentle or slower. Reducing combustion noise to some extent. Just what I think. Not proven.

So I pulled all the injector return lines one at a time and there was no change in the noise. Air cleaner mounts look solid, and the noise seems to be coming from under the valve cover. Should my next move be to pull the valve cover and go ahead and plan on adjusting the valves while I take a look?

Do a cold valve adjust ~ once I apparently left a lock nut un snugged and a valve began to tick noisily .

FWIW : tight valves are silent as they burn .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

It runs better off of diesel purge because of the higher levels of cetane than fuel. It's a more complete combustion and can mask bad injectors, or other related issues to fuel. It's great for diagnosing fuel issues. I'm not sure why oil combats better and makes the engine quieter. I'd assume lubricity properties.

@ the OP. Why did You remove the injector lines and not crack them just a quarter turn? Also, your next step should be to do the valve adjustment with feeler gauges.

__________________
Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

Yes, but because it burns so well it also gives you the same "fix" if you have bad compression, incorrect timing, et cetera. So if it runs quieter no matter which you have I don't see how it's automatically a fuel problem. It could be any of those.

-Rog

Mainly because I have no idea what I'm doing. I pulled the injector lines off all the way, which made me realize I need new lines. Going today to pick some up.

If I wanted to adjust the valves in the next day or two, are there any stores that sell the adjustment wrench or do I pretty much need to look online and wait for shipping?

Order them online. Why do you say you need new lines? Are you talking about the metal hardlines? If you aren't sure of what you're doing, before you do anything, ask questions! Before you break or make a big mistake that could cost you the engine. Before you do tbe adjustment, do consult.

__________________
Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

I've never seen it correct compression. if compression is bad enough the purge wont mask it. Same with timing. It's mainly used to mask poor nozzles. I only say that cause I did it on my 92 300d before I swapped it and it didn't mask the low cylinder compression misfiring.

__________________
Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

No, that's wrong. The return lines are only there to return any unused fuel to the fuel system. The correct test is to loosen the nut of the metal injection line at the top of the injector. I believe it is a 14mm nut.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

On the OM60x engines it is 14mm, but on the older diesels I think it's 17mm. Either way the hard injector line has to be loosened, not the rubber fuel return line.

The OP needs to pay attention to what is being said by people trying to help him. There have been multiple iterations of the same suggestions that have so far gone completely ignored. It's really hard to help someone who refuses to help themselves.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]