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Discussion Starter #1
Hey All,

Noticed this weekend a strange squeal when slowing down to a stop. Don't think it's brakes as it will occur even if not touching the brakes. Additionally, letting off the brakes doesn't change the sound. I don't believe it happens when accelerating. The sound is fairly loud and doesn't go away until about stopped. I almost sounds like the noise is more related to the engine than the chassis as the sound changes more as the engine is slowing from about 1100RPM's to idle. Strangely I can't seem to reproduce is while stopped by revving the engine. It's so strange. If I accelerate to say 15 MPH and then let off the throttle and slow own either by using the brakes or just letting the truck coast and slow down the sound will happen. Before I go an drive myself nuts trying to diagnose the problem I figures I would ask if anyone else has ha a similar experience.
 

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Not using the AC are you, while this is happening? I ask because another member posted a thread here in the general discussion area called "Intermittent AC Problem" and he says there that he experiences a loud whine which he originally thought was the transmission, but found that his AC was blowing warm, so now believes it to be that.
 

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Discussion Starter #4
just under 20,000 miles, 2017 Colorado Z71. Over the weekend when I first noticed it I was towing and I didn't have the AC on. Yesterday I think I may have had the AC on. It almost sounds like something slowing down. Like you are at 1500 MPH and when the engine goes to idle whatever the sound is is a spinning sound that's slowing down. As mentioned, I'm pretty sure it's no the brakes since the sound occurs even if not hitting the brakes and hitting them make no change to the sound. Initially I thought maybe the fan clutch but it doesn't seem to happen when accelerating or revving up the engine. I need to pick something up from the store so I'm going to try to make more observations.
 

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Could be a pulley or idler I suppose. Maybe when you are on the accelerator, there is load/tension on the belt/ pulley, but once you let off, there is no load so it is load/ tension.
 

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Discussion Starter #6
OK, riddle me this Batman cause it makes no sense to me. just went out to pick up some things at the store as well as to get fuel. It's doing it from the start of my trip. Last on the trick is the BP station for diesel. I fill up the tank and decide to turn on OBD Fusion and check soot level, guess what, I'm in active regen. So I take it up on the highway for 20 minutes to get thru regen. Get off highway and it's no longer doing it. I have no illusions that the active regen is what's doing it but it is strange. It was doing it while towing over the weekend by the time I got home and the DPF was about 80% full. I'll have to keep monitoring it, to me it seems more chassis related than engine. I did try at 30-40 MPH and popped it into neutral, nothing. Tried again at 25, neutral and it only started once the truck got to about 10 MPH, this was all before the highway trip to complete the regen.
 

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Hey All,

Noticed this weekend a strange squeal when slowing down to a stop. Don't think it's brakes as it will occur even if not touching the brakes. Additionally, letting off the brakes doesn't change the sound. I don't believe it happens when accelerating. The sound is fairly loud and doesn't go away until about stopped. I almost sounds like the noise is more related to the engine than the chassis as the sound changes more as the engine is slowing from about 1100RPM's to idle. Strangely I can't seem to reproduce is while stopped by revving the engine. It's so strange. If I accelerate to say 15 MPH and then let off the throttle and slow own either by using the brakes or just letting the truck coast and slow down the sound will happen. Before I go an drive myself nuts trying to diagnose the problem I figures I would ask if anyone else has ha a similar experience.
I was experiencing the same exact thing and have just over 18K miles. It was driving me nuts. It sounded like a belt or pulley as it was only happening under 1200 RPM when slowing down or going around corners. Once I get over 15 or 20 mph or higher RPM I didn't hear it. I popped the hood to see if I could hear at idle it wasn't consistent unless in gear which means a load on the engine with auto AC on. When I popped the hood I noticed a ton of mud had splashed up into my engine bay from the last desert trip so while the engine was running, I sprayed the entire engine compartment with a hose (not super high pressure) but enough to knock some of the mud and dirt off everything. I let it continue running and then took it for a drive and the noise had stopped. My guess was just some debris on the belts. That's just my $0.02
 

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Discussion Starter #8
Thanks for the information. I don't think my truck's ever been off road but it's worth a try for sure.

I'm going to check the brakes. Even though the squeal doesn't seem to change with me hitting the brakes I should probably just check the pads. I feel like the sound is definitely chassis rotation vs. engine rotation.
 

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Sounds like what my truck is doing, took me forever to isolate the problem, I haven’t listened to the radio in ages. I replaced the fan clutch, but mostly because it was shot. My real issue is the A/C making noises when slowing down to idle, otherwise I can’t hear it. I have heard intermittent noises when I turn my AC off while at idle after driving. I am just going to let it go until my A/C stops working and then replace it. My truck is at 90k, so it’s out of pocket for me anyways. I would just play with driving with and without AC and see if you can isolate the noise. Hope that helps.
 

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Discussion Starter #10
I've tested it a bunch of times and the AC doesn't appear to have any effect on the noise. It's pretty consistent at slower speeds regardless if AC is on or off.
 

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Discussion Starter #12
Interesting. Mine has disappeared since originally posting. Previously I would have said the first 2 spots at the front hub and transfer case wouldn't make sense unless in 4WD since they don't spin and I've never engaged the 4WD but since then I've realize my knee keeps hitting the 4WD selector so I find myself in auto and even 4WD sometimes so maybe there is some truth to it.

If my squeal comes back this will be the first thing I try!
 
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