What does the beginning of vacuum pump failure sound like on a 603?
 

heard a vibrating sound coming from under the hood, (Yes i have a Diesel HAHA:D) I could trace it to the front of the engine but farther then that I cant tell, its a 87 300D, it only makes the sound a a idle, if I sped on the GO pedal it goes away, Its not a vibration I can feel per say, Its more of a sound I can hear even in the cabin.
I have heard the horror stories of 61X engines and the way the pumps fail, dropping the ball bearings into the timing chain area and then causing full destruction. is it the same thing on the 60x engines? the car doesn't show any signs that I can tell of having vacuum issues. good brakes, instant shut down. I dont know if this is a serious issue?

I felt no vibration and heard no noises prior to my pump failure that shattered the valve cover/cam...
noise, pull the belt tensioner and the VP, and figure out what's causing it.

Are there any videos on pulling the Vac Pump on a 603?

I agree with VSTech. I had 270,000 miles on my om 603 before I replaced the vacuum pump...and I'm glad I did. The bearings looked like they were about to fall apart. There was no discernible difference in noise before or after I changed out the pump. If yours is the old style cover (crimped on without any screws) then you should probably change it just off principle. There really seems to be no way to predict when it might fail.

you won't need one, just pull the belt, and rotate the tensioner out of the way, then take off the hard vacuum line, then remove the bolts around the perimeter of the pump. and remove.

I find it easier to remove the tensioner all together, because every one I've pulled out was bad as well... 12mm allen socket for it.

easier to pull the tensioner first anyway, because if you have to rotate the engine to relieve tension from the pump ramp, the tensioner will bind on the balancer...

The risk of continuing to use the older design vacuum pump as the miles build is palatable. Even getting the newer design with the ball bearing retainers from a pick and pull is a better option than sticking with the older design of pump.

It is just something that should be replaced since not doing so can be very costly. It can be visualised as a potential ticking time bomb as the overall milage gets high.

Replacing the pump is no big deal. I had to do it twice within a week not too long ago on my 300SDL, because I stripped off the head of one of the two bottom bolts torquing the pump down the first time. I removed the fan clutch, fan shroud, upper rad hose, the part of the belt tensioner that is bolted to the head. Maybe a little more work than needed, but it was a fairly easy job. There is a great sense of relief knowing that it won't explode on me at any second. :D

Make sure to crank the engine properly when you take it off, and put it back it on. Mainly putting it back on, you don't want to crack the pump.

noise at front of engine
 

All that about the vacuum pump is good, but my 603, I've went through 2 belt tensioner shock obsorber. The rubber in the attachment end where it bolts to tensioner failed. Even the 1st replacement only last less than 100 miles.

I was able to (I believe) source the noise, I noticed that my belt looked like it was shaking, then I noticed that the shock absorbers when moving quite a bit. and it sounds like that is where the noise is coming from, but while im in there I will pull the Vac pump also.
Thanks once again for all the help and suggestions.:)