I just recently had my starter replaced and now the mechanic is saying that my 2012 Mercedes GL450 is running loud and will not accelerate. What went wrong?

What is your question?

There were no prior issues of the vehicle running loud nor slow acceleration prior to the starter being replaced.

What makes this problem better or worse?

Starter

How long has your 2015 Mercedes-Benz GL450 had this problem?

week