Vibration and Groan after Auto Start/Stop
 

I was wondering if you guys might try this in your car. The engine is fully warmed up and you come to a complete stop. The engine shuts off. If you lift your foot slightly, where the engine fires up again, but you are still stationery, can you check if after 2 seconds or so, the engine will groan and make this odd sound, and send vibrations into the passenger compartment?

Maybe vibrations from the torqu converter?

I think this may be common but people miss it because you usually accelerate after the engine fires up so you can miss this entirely. I forgot to mention it lasts for about 2 seconds and then returns to normal. It reminds me of when you turn on an AC compressor in an old car, and how it puts additional strain on the engine.

Both my cars do that, I think it's powertrain backlash. Have got use to it. It really does it if I stop and put the car into reverse

Did you ever figure out what it was? My 2016 E350 Wagon is doing it on start stop. Same groaning sound.

I have auto start-stop disabled the week I bought mine. I haven't had any experience like that. Is this normal or does it mean service is needed?

2016 E350 wagon with M276engine, 82,000 miles. Normally we press the ECO button after starting the car, but when we forget, and the engine tries to restart at a light, it makes the groan for 2 seconds.
This just started happening, out of warranty, I know I can buy programming tool and have the ECO mode stay off permanently. But the bigger question is - what is it?
I've read Transmission mounts (easy repair?), Motor mounts (Difficult repair), and also timing/check valve in cylinder (seems unlikely) .. Is it just the starter motor? some sort of starter motor clutch?