My 1997 SL500 makes a metal against metal clank sound under the front end when accelerating from a slow rolling coast type speed. From a dead stop- no such sound. Hoping to head off a costly repair . Suggestions please.

Can you see anything hanging from under the car that might make racket underneath when enough wind catches it (like from a rolling start vs. no wind from a standing start)? Just a WAG. Good luck.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

Loose cat heat shield?

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

Thump-Thump-Thump w/ slight metallic ring? Gets faster and then stops?

Check the lug bolts on the alloy wheels, on my 300E they had a worn shoulder that made then loosen up a scoche - just enuff to get the wheel a smidge off center on the hub and that's what the tapping is. One wheel where the wheel is slipping on the hub and tapping the lug bolt.

Tightening with 1/2 in breaker or 4 way wrench is good, Milwaukee V28 is better...

Thanks guys but sounds much more severe.Like 2 heavy cast pieces banging together under engine. Hope this helps.

Don't be over-tightening those lug bolts.

And don't let them tighten the lug bolts with an impact wrench at the tire store, either.

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2012 E350
2006 Callaway SC560

Just had to replace both motor mounts on my 1970 Chevy. When I accelerated just right, the fan would contact the shroud due to engine torque raising the engine. It made a ringing metallic sound. Don't know why yours won't do it from a stop though. Worth checking I guess.

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1983 M-B 240D-Gone too.
1976 M-B 300D-Departed.

"Good" is the worst enemy of "Great".

I had a '69 Chevy that did that. The motor mount broke in half and one side of the engine would come up. I thought all the replacements had a sort of hook inside where they could not get loose.

The best part about when mine did that? The throttle would stick open because the linkage would bind when the engine twisted out of place.

I've never seen a MB mount do that, though.

They usually sink. Maybe the fan is hitting the bottom of the shroud.

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2012 E350
2006 Callaway SC560

Yeah, when my 124 mounts went bad the engine just kind of sunk down and the thing vibrated a lot. I'm just kind of grabbing at possible solutions.
And I'm with you on that binding throttle linkage thing! The more you rev it the more it revs itself! Not long after my model they started using throttle cables instead of solid rods and I can't help thinking that might have been part of the reason.

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1983 M-B 240D-Gone too.
1976 M-B 300D-Departed.

"Good" is the worst enemy of "Great".