Clunk sound in back

Had my 1993 Astro Ext for about a year now, I really think it is a fantastic vehicle. One thing is getting to me though, when going slow I get a clunk sound from the back of the van when gear changes happen (soundsas if it is somewhere near the diff), its not loud and doesn't happen in all the gears. Anyway I thought it might be the universal joints, so I had them changed but the clunk is still there. My mechanic says there might be a problem with rear axle end-float. (But he is an English mechanic who is not very familiar with US vehcles). Does anyone have ideas what the noise might be? Thanks for reading this.

If it's a floating rear axle then it will probably make some noises. I have an 84 GMC Jimmy with a floating rear axle and it makes noises too. If that's what it is, then there's nothing to worry about. Does the van jerk or anything? Can you feel the clunk, or just hear it?

Thanks for taking the time to reply. I'm not sure but I think the Astro has semi-floating back axle. It is only a clunking sound – no jerks or pulls whatever.

It's probably nothing to worry about if it's a floating-rear axle. I would, however, have the diff fluid changed so you can have it checked for shards or flakes or metal. Good luck.