My '90 clicks all the time. It has "ADS" adjustable damper system. I can hear electronic-type clicks from somewhere under the car at very regular intervals. Main dealer could not diagnose anything wrong. Car seems to be behaving properly, so I'm not concerned. If you find out what it is please let us know.

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'66 W100 600 SWB
'05 W463 G55K AMG
'91 W126 500SEL
'93 W463 300GDL
'84 W460 280GES
'83 W460 300GDL
'66 W111 220SEb Coupe
'58 W121 190
'58 W180 220S
Have previously owned '99 SL600, '99 ML320, '79 450SLC, '79 450SEL 6.9 x 2, '68 600, '91 190E 1.8, '90 190E 2.0, '85 190, '90 500SL, '92 500SEL, '97 E300Turbodiesel, '91 300D, '72 280S, '82 300D, '81 300SD, '85 230E, '56 220a and I'm sure I'm forgetting some.