Quick loud squeal noise on downshift
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Newbie
Joined: May 2024
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C204 c250 coupe with AMG upgrade pack
Quick loud squeal noise on downshift
Hello guys!
just noticed a (drive belt like) squeal coming from my car (C-Class c204 C250 M271 722.9 transmission) on downshifts
only happens when I’m downshifting at high rpm’s or in sport mode.
however my transmission isn’t jerky nor does it slip.
(it can’t be the drive belt as I have a new one in)
I don’t hear it when parked and bringing the engine rpm up higher.
i did notice my wheel bearings have to be changed but I’m not sure that’s it.
The sound can come one regardless of cornering, going straight, up or down hill doesn’t matter it’ll do it.
does anyone know what’s going on?
just noticed a (drive belt like) squeal coming from my car (C-Class c204 C250 M271 722.9 transmission) on downshifts
only happens when I’m downshifting at high rpm’s or in sport mode.
however my transmission isn’t jerky nor does it slip.
(it can’t be the drive belt as I have a new one in)
I don’t hear it when parked and bringing the engine rpm up higher.
i did notice my wheel bearings have to be changed but I’m not sure that’s it.
The sound can come one regardless of cornering, going straight, up or down hill doesn’t matter it’ll do it.
does anyone know what’s going on?
Last edited by Jakey180; Apr 26, 2025 at 05:54 AM.
MBWorld Fanatic!
Joined: Aug 2023
Posts: 3,687
Likes: 1,107
From: MA Coast
W204 2010 C300 4matic Sport M272
Cant really say that it cant be X because its new. It still could be a faulty part or the wrong one. Not saying its your drive belt, just saying you cant rule it out until you rule it out.
You mention it sounds like a drive belt. If it were me I would put the old drive belt back in and see if the issue still occurs. When I replaced my drive belt I kept the old one in the trunk just in case.
Did the issue start after you replaced the drive belt? What other work have you done to the car recently if anything?
What size, brand belt did you install?
You mention it sounds like a drive belt. If it were me I would put the old drive belt back in and see if the issue still occurs. When I replaced my drive belt I kept the old one in the trunk just in case.
Did the issue start after you replaced the drive belt? What other work have you done to the car recently if anything?
What size, brand belt did you install?
Super Member
Joined: May 2024
Posts: 505
Likes: 122
From: Northern Indiana
2014 c300 w204.080 3.5 v6
You don't say your year or engine but if you have the 276 v6 engine it could be the PCV system that has a torn diaphragm. Especially if it only squeals when hot.
Thread Starter
Newbie
Joined: May 2024
Posts: 5
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C204 c250 coupe with AMG upgrade pack
Thread Starter
Newbie
Joined: May 2024
Posts: 5
Likes: 0
C204 c250 coupe with AMG upgrade pack
Cant really say that it cant be X because its new. It still could be a faulty part or the wrong one. Not saying its your drive belt, just saying you cant rule it out until you rule it out.
You mention it sounds like a drive belt. If it were me I would put the old drive belt back in and see if the issue still occurs. When I replaced my drive belt I kept the old one in the trunk just in case.
Did the issue start after you replaced the drive belt? What other work have you done to the car recently if anything?
What size, brand belt did you install?
You mention it sounds like a drive belt. If it were me I would put the old drive belt back in and see if the issue still occurs. When I replaced my drive belt I kept the old one in the trunk just in case.
Did the issue start after you replaced the drive belt? What other work have you done to the car recently if anything?
What size, brand belt did you install?
Repco - 6 rib x 2315mm
Joined: Nov 2016
Posts: 7,847
Likes: 3,495
From: Maryland
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Grab some belt dressing at Walmart or your local auto parts store and give it a squirt. If the noise goes away, it's your belt.
