Rattle at idle - only in drive and reverse
Thread Starter
Newbie
Joined: Apr 2024
Posts: 4
Likes: 0
From: Atlanta GA
03 E320, 2002 BMW M3, 2023 BMW M3, 2021 Model Y
Rattle at idle - only in drive and reverse
Hello. I just bought my first Benz and have typically been a BMW guy. This E320 was too clean inside and out to pass up for the price seller was asking. So far, I have fixed engine mounts, headlight lenses, and given it a 1 step paint correction.
My current issue I'm looking to tackle is a rattle that comes from front of engine near drivers side and only happens in drive and reverse but with the brake applied. It starts to fade as I start crawling again such as if one is driving in traffic. It also becomes less as the engine warms up but is at its quietest after 20 minutes or so of driving and I think this is more so because the engine becomes smoother at that point (this one, anyway).
To date, I have looked at the lower engine covers and some of the exhaust heat shields. I have not yet been able to rule out anything in valve train or drive belt pulley area. Any one has this type of rattle that can provide some suggestions on where to look?
Link to video -
My current issue I'm looking to tackle is a rattle that comes from front of engine near drivers side and only happens in drive and reverse but with the brake applied. It starts to fade as I start crawling again such as if one is driving in traffic. It also becomes less as the engine warms up but is at its quietest after 20 minutes or so of driving and I think this is more so because the engine becomes smoother at that point (this one, anyway).
To date, I have looked at the lower engine covers and some of the exhaust heat shields. I have not yet been able to rule out anything in valve train or drive belt pulley area. Any one has this type of rattle that can provide some suggestions on where to look?
Link to video -
MBWorld Fanatic!
Joined: Jun 2014
Posts: 1,088
Likes: 447
From: Melbourne, Australia
2010 ML550 VIN WDC1641722A564750, 2010 B180
My first thought is that its the tensioner arm on the serpentine belt. The tensioners are at their lowest level of tension when at idle as opposed to when the engine is at a higher rpm. When they fail, they become noisy similar to the sound youve recorded. That might account for the difference when you accelerate - tension rises due to higher rpm and the noise ceases.
Noting you comment on the brakes, if you release the brake whilst in drive, say on a hill, so the car doesn't move, does it make any difference? I assume braking performance is satisfactory.
Noting you comment on the brakes, if you release the brake whilst in drive, say on a hill, so the car doesn't move, does it make any difference? I assume braking performance is satisfactory.
Thread Starter
Newbie
Joined: Apr 2024
Posts: 4
Likes: 0
From: Atlanta GA
03 E320, 2002 BMW M3, 2023 BMW M3, 2021 Model Y
My first thought is that its the tensioner arm on the serpentine belt. The tensioners are at their lowest level of tension when at idle as opposed to when the engine is at a higher rpm. When they fail, they become noisy similar to the sound youve recorded. That might account for the difference when you accelerate - tension rises due to higher rpm and the noise ceases.
Noting you comment on the brakes, if you release the brake whilst in drive, say on a hill, so the car doesn't move, does it make any difference? I assume braking performance is satisfactory.
Noting you comment on the brakes, if you release the brake whilst in drive, say on a hill, so the car doesn't move, does it make any difference? I assume braking performance is satisfactory.
MBWorld Fanatic!
Joined: Jun 2014
Posts: 1,088
Likes: 447
From: Melbourne, Australia
2010 ML550 VIN WDC1641722A564750, 2010 B180
If the a/c makes it worse, even momentarily, then it's a safe bet to examine the belt and pulleys. The extra tension required momentarily when the a/c compressor kicks in is the sign. Check your belt as well. Not sure they're known to stretch (I'd say they'd crack amd break first) but if it's got more than 70k miles on it, it's not bad maintenance anyway.
Check your a/c compressor clutch operation as well. Quite possibly thats your problem.
Check your a/c compressor clutch operation as well. Quite possibly thats your problem.
Thread Starter
Newbie
Joined: Apr 2024
Posts: 4
Likes: 0
From: Atlanta GA
03 E320, 2002 BMW M3, 2023 BMW M3, 2021 Model Y
Thread Starter
Newbie
Joined: Apr 2024
Posts: 4
Likes: 0
From: Atlanta GA
03 E320, 2002 BMW M3, 2023 BMW M3, 2021 Model Y
Closing this out. So the tensioner wasn't the issue but the drive belt instead. It had stretched enough to take the tensioner close to its max threshold but was still tight enough to not slip or fall off.
