03 GLE, 152xxx miles. Happened only twice in about 6 months of owning the car but those 2 times were in the past month. I'll put the car in reverse and get a very audible rattle from behind/next to the drivers front tire. Has happened only in reverse and I never hear it in other gears. (Auto trans) sounds very metallic, but not like a lose item hitting another. Could it be the mount right there? Or possibly a trans issue....? Both times it happened it was fairly cold out.

 

Could be possible that your timing chain tensioner is starting to go out. The low idle of the reverse gear causes more vibrations & makes it more audible.

 

But I don't hear anything like this at all in park, neutral, idling in drive, or driving. Only in reverse, and accelerating in reverse doesn't make it go away.

 

Are you parked on a incline and not using your parking brake?

 

TC is on the opposite side.

Can you tell if its engine related, chassis/suspension related, exhaust related? A little bit on the vague side for the description.

 

Nope it's been flat ground both times and I do use the parking brake even though it's an AUTO trans but only when it's warm out (so that the brake line doesn't freeze over night)

And it's kind of hard to be overly specific but I'm positive it's not engine related. When it did it I put the e brake on and looked under the hood and the engine sounded perfectly normal, it was definitely coming from somewhere near the mount under the airbox.

 

check the exhaust heat shields

 

If it's coming from your wheel area it could be the dust cover behind your rotor. If you've been working in the area you could have bumped it, which is easy to do if you're not paying attention. If not maybe by chance a stone hit it. When that happens it's usually more of a on/off metallic grinding noise though. I say on/off because I believe it rubs the rust ring on your rotor which isn't even. It could cause vibration though if that shield is touching the rotor when you stop to change gear out of reverse. Anytime that has happened to me it's only happened in reverse while turning, like out of a driveway for instance. If you've never heard that distinct sound it may be worth a shot to peel the dust cover away from the rotor.

 

The only work done on the rotors was when I first bought the car about 6 months ago and that was only to cut away the rust on them and it was done by a highly trusted friend of my dad (absolute car freak who owner a car just like mine) with a professional brake lathe. The sound is definitely coming from somewhere in/near the engine bay.

 

Bad mount would cause vibration but as for the rattle I'd agree with heat Shield. If it sounds like its from the engine bay possible the shield over the manifold. When the cars cool try giving it a few taps to see if it's loose.

 

So there's a possibility the mount could be causing vibrations which in turn cause the rattle? If that's the case then I'll just replace both to ensure the noise is gone.

 

So I was driving around and noticed the noise but luckily had someone with me to hold the car in place while I checked it out. I went to open my hood and discovered...it IS the hood. One of the hinges is loose and rattles right where I always hear the sound, I guess the combination of low rpms in reverse and the wonky hinge make the rattle.

 

In reverse the engine torque raises the exhaust system...more than likely a heatshield being contacted due to wornout exhaust hangers!

 

I just recently had the entire catback replaced along with all New hangers

 

I'm having a similar issue. Its only when I dont give it a good bit of throttle and when I engine brake in 1st 2nd or 3rd. If you figure out what it is lemme know so I can check it out!

 

Engine brake?

I discovered that it was the latch on my hood which was loose. The cold combined with such low rpms at idle or in reverse cause it to pulsate and make the sound. New latch and hydraulics and it's all gone.