As of late, my 1987 300D Turbo has developed a bit of a tapping or knocking
noise that's only really audible at idle, not quite on every cylinder firing
but it's very steady and noticeable. It used to be a few seconds on, a few
seconds off, but now it's consistant at idle. I recently did an oil, oil
filter, and fuel pre-filter (the small plastic rough screen filter) change
but was unable to locate a new canister fuel filter. Could this tapping
noise be water in the fuel filter (which I am going to replace tomorrow), or
possibly some erroneious lifter noise with the new lighter weight oil (went
from generic 20w50 to Delo 400 15w30)?
Any advice greatly appreciated!