I have a 300D W124 1993 with a very slow speed thump-thump-thump in the rear. I rotated the tires, and the Thump-thump-thump is still in the rear. It happens from zero to 5mph and then will smooth out. I've brought it to a garage and they think it's the rear knuckle/spindle just from the wheel when on a lift being able to 'wiggle' when rocked from the 12 and 6 o'clock position. The spindle/knuckle is expensive and difficult to find. I"m wondering if it might be the 5 point arms with rubber mounts that attach to the spindle. Is there any test to find out easily? Thank you.

get a 2nd opinion. a rotational noise is not normally in the suspension but the wheel, tire, axle and/or bearing.

sounds like a broken shock mount. My kid's BWM did same thing from the back end.

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dtf
1994 E320 Wagon (Died @ 308,669 miles)
1995 E300 Diesel (228,000)
1999 E300 Turbodiesel ( died @ 255,000)
2006 Toyota Tundra SR5 AC 4X4 (115,000 miles) rusted frame - sold to chop shop
2011 Audi A4 Avant (165,000 miles) Seized engine - donated to Salvation Army
BMW 330 xi 6 speed manual (175,034 miles)
2014 E350 4Matic Wagon 128,000 miles
2018 Dodge Ram 21,000 miles

the low speed thump thump noise without road roughness on a W124/W201/W210/W140 is usually the driveshaft support bearing and its rubber hanger.

quite easy to diagnose too.

Anyway - if the rear spindle is moving - its usually the toe link or the camber link bushings - need to replace entire arms. Make sure the whole spindle is moving and not just the hub and wheel which means a bad wheel bearing (not too bad on a sedan with an in situ kit (front wheel drive bearing cup set) you can rent from autozone now.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)