Just some advice from my 2 300sd's -- maybe same for your car?....
I'm not a mechanic but I've changed quite a few pads. I started doing my first brake job 5-7 years ago.
In general, make sure you use good quality pads -- i.e. textar from fastlane works good for my 300sd and I believe they are the OEM for my car. Don't buy from a local parts store - I found "Raybestos" pads (don't ask me why...) are not good for my car and caused the pads to overheat.
I used to have screeching problems but then realized I needed to use some type of silencer material
Also use some brake pad paste (at the dealer they'll give you small packets of it if you buy their pads, or get "Disc Brake Quiet" from Pep Boys. It comes in aerosol spray. Works excellent - I spray it to the pads before inserting waiting 10 minutes. Its a blue colored spray material that works well.
Never heard a "grinding noise" -- usually squeaking high pitched sound if you are lacking paste/silencer material...maybe someone else can help out. Is it pulling to one side when you brake...that happended to me once and I found that the problem was a bad brake caliper that was sticking.
1) 84 300SD 285K+ Miles (Ver Calif)
2) 84 300SD 175K+ Miles (Ver Federal)