Horrendous whining sound and clear liquid leaking from underneath car!!

[Cozens88]

Can anyone help, just done a 200 mile trip back from London and about 20 mins from home I get this horrendous whining sound coming from what appears to be the middle of the car. The sound stops when at standstill and in reverse. Once I got back, I checked under the car and there’s a clear liquid leaking out! It’s not oil or tranny oil, break fluid level is also fine. No engine management lights are showing either. Car is a E220D AMG (Auto) 2017 W213!

I’ve linked a video for the sound I’m experiencing and of the leak!

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[Fununcle]

Are you sure the clear liquid is not the condense from the air conditioning and not related to the noise?

 

[Cozens88]

Are you sure the clear liquid is not the condense from the air conditioning and not related to the noise?

Just fired it back up this morning, no air con on and car only running for 30 seconds and the fluid is still leaking out.

 

[Fununcle]

Bugger

 

[Bellow]

The sound stops when at standstill and in reverse.

Downstream from the gearbox then. Anywhere between it and the tyres. I'd check propshaft for anything tangled in it but not before I'd checked the brakes for a trapped stone. (Raise each wheel off the ground one by one and see if the noise emanates from any of them. If so, rotating the offending wheel backwards may be enough to dislodge anything trapped).
The fluid leak - establish what fluid (smell/taste) and be open to it being entirely unconnected to the noise.

 

[TeddyRuxpin]

Great advice from @Bellow. Yes, stick some tissue on the fluid and smell it!

That noise does sound like a stone in the brake shield - does the pitch change as you accelerate? What about in neutral and revving the engine? This will help you figure out if it's engine related or not (doesn't sound like it).

 

[JHS]

I had the same noise, never really did find out what it was. Came on suddenly for a day and went just as suddenly after I braked sharply. I suspect a stone.

 

[rf065]

I had a similiar noise on my CLK when the rear brake back plates has rusted, they hold the springs for the handbrake shoes. Assume yours has the electric handbrake? Not sure if the cause could be the same though?

 

[Bayleaf]

Could it be the water pump has locked up and the belt is screeching.
The fluid could be water.

 

[JHS]

Could it be the water pump has locked up and the belt is screeching.
The fluid could be water.

Quote from the OP "The sound stops when at standstill and in reverse."

 

[SpikyMikey]

I had a similar issue on one of the vans once - small stone jammed between rear caliper and disc. A nifty bit of high speed reversing dislodged it.