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'88 GMC Vandura clunks and clatters when starting

This machine makes a loud clunking sound when starting. It always starts, runs fine afterward, and oil pressure is very high, as it has been. But the clunking is quite solid sounding, and dissipates over about the first ten seconds, then engine runs smoothly. If I restart it, there is no odd noises, until it cools, and it begins all over again.

By phone, one mechanic speculates it may be the flywheel assembly, which is where the sound seems to come from, or the oil pump inside the pan. Another suspects it may be the catalytic converter that is worn out and disassembling internally.

Van has a wonderful 250,000 miles on it, has been well-cared for, but never replaced the Cat. Conv. Too many miles to spend much money on it. ???

Did you ever get a response? I was going to post a similar question…I have an 88 GMC G25 Vandura (Starcraft) which I bought in Alaska in July (spent a bunch of $ getting the engine tuned up and new shocks) and drove back down to Wisconsin. Now with 195K miles. 14.5 mpg crosscountry (what do you get?). Just in past week when I start it up and drive it a few feet, I hear the loud clunking sound…and immediately stop since I don’t know what is happening. It comes from the front left it seems. I jacked it up and took off the front left tire thinking something was loose in the drum, but nothing found. It does not change when braking so not that. Let me know if you find the source of the noise. jhfour(at)gmail