How to diagnose a vibration and rumble on Mercedes

Here is a 2013 Mercedes with about 100k miles and has a vibration at idle/neutral from about 1500 rpm to 4000 rpm range. Also, noticeable when driving. Taking the weight off the transmission mount can reveal if it's weak. This one isn't as bad as the ones I've diagnosed before. Sometimes shops replace the harmonic balancer or front engine mounts, for a lot of $$$ before realizing it's only the trans mount!!