My Volvo did that for a while, then refused to crank, fortunately in the drive at home.

When I got around to taking the starter off to exhange it, I found the battery cable loose. Took it off, replaced the washers, and it's been fine since. Loose connection had burned the cable and washers to the point it quit conducting.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!