Hey everybody, I really need some help on this one because I am clueless. My 240 is making a clinking sound when it is running, even when it is idle. It sound like a high pitched metal clinking sound that happens 2 times a second. I am baffled, but if you guys have some suggestions I would love to hear them

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1981 240D/297K/4-spd/OM617 (mine)
1982 240D/241K/4-spd (wife's)
1979 240D/291K/4-spd/OM617 (father-in-law's)
1983 300DT/240K/4-spd (brother-in-law's)
1985 300DT/???K/5-spd Intercooler conversion (brother-in-law's)
1985 280TE/160K/5-spd (father-in-law's)
1963 UNIMOG (brother-in-law's)