'17 Regal-new sounds and vibrations

[Bobcat2017]

Got 95K miles. Started picking up on some weird sounds and vibrations.

The car would shimmy between 40-60mph on smooth roads. No more, no less. When going over bumps, RR Xings, manhole depressions etc, a sound pops up every now and then that sounds like pebbles being rattled in an empty milk jug. The sound lasts no more than 5 seconds and I do nothing special to make it stop. Sound most frequently occurs in the rear but happens in the front too

All items were removed from the car + trunk. Replaced shocks, struts, springs and mounts in front and rear.

What am I missing?

 

[Malo83]

With all those replacements, was everything tightened down properly and torqued. 😉

 

[bugspop1]

That's a great question Malo83.
Unless you do the work yourself you can never be sure.
But even if you've done the work yourself, it wouldn't hurt to doublecheck your work .

 

[Bobcat2017]

With all those replacements, was everything tightened down properly and torqued. 😉

Yes, it was looked over by 3 different mechanics

 

[bugspop1]

The Car Shimmying at around 40 to 60mph sounds like a Broken Belt in the tire.
Broken Belts in the tires will usually make a humming noise, not sure about a rattling noise?

Have you looked at the Sway Links, they can make a rattling noise when they are bad.

The Suspension Coil Insulators could be bad too, they can make all kinds
of racket in the rear end too, but you said you replaced the Coil Springs so I'm betting
you replaced the Insulators if they were worn out!

Strut Mounts would normally be something to look into for the Rattling Noise, mainly
heard when turning, plus you said you've replaced all that in the front end.