'97 E300 sounds like marbles...
 

My E sounds like marbles when it cold. Added a full bottle of PrimeRose all-season fuel additive to help rid of any water if there is any present. I tanked up a few weeks with the Global Premium Diesel, as they claim at a local Global in Glastonbury. After 3 tanks I notice severe oxidation of the new fuel cap. Had the fuel cap for only a year and it is rusted bad. Have gone back to my usual Hess for the last two tanks.
I'm thinking of taking a trip to BurkeOil outside of Boston to top off with some BioDiesel and filling a few 5 gallon containers to help clean out the fuel system. Would this help? I don't want to pull the injectors at this time nor have the time to do it.

I've noticed that the last two tanks my mileage has turned into garbage. Is it because of the winter fuel changeover? Before even with the sever rust on the cap on my last tank of Global fuel my mileage hadn't changed but knocking did increase. Granted the weather is getting colder but I don't remember my mileage being so drastically affected or knocky, only when it was freezing cold.