2006 Mercedes-Benz E-Class - Back end issues

My back end whines really loud or sounds like road noise after relaxing tires and also alignment

Relaxing? Or replacing? Not sure what you mean

Probably “replacing.” I suspect autocorrect gone wrong. Anyway, tires with different tread can make a different sound when you’re driving. Beyond that, it’s possible the differential is making some noise. The OP can have it checked out for peace of mind.

If the tires are a change, have them mounted up front so you listen for the noise to move. You want to target or eliminate the tires. Tires are cheap compared to the rear differential.

Additionally, the rear wheel bearings could be the source of the noise.

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That would also be my assumption