High pitch whistle when accelerating over 40 mph

[Russell Balzan]

2001 TJ - 4.0L Inline 6 - when I reach 40mph, a high pitch whistle starts. It seems to fade in and out as the accelerator is pressed and then even when it isn't. Once I hit about 75mph (highway speed limit in AZ) it goes away (or I can't hear it due to normal noise). Any ideas?

 

[Chris]

Sounds like a u-joint. Try greasing all of them and see if that helps. It could be a unit bearing as well, but those are usually more pronounced when making turns.

 

[jchadscud]

Also check any light bars or other accessories that could be catching wind and causing noise.

 

[Jake Portillo]

Do you have a cold air intake? Mine does that through every gear if I’m not mashing the throttle.

 

[Stox5225]

My wife’s 2001 XJ does that ... I think it’s HVAC related.


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[fourpointzero]

Vacuum line, I would have guessed too. However, this happened to me but in the deep winter. Was a loose bolt on the pipes (upper cats exhaust)that attached to the manifold. Can very well be the one closest to the engine firewall.


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[Mr. Bills]

The description sounds like a CAI whistle as @Jake Portillo suggested. Do you have an aftermarket air cleaner assembly?

 

[Russell Balzan]

this is a very stock jeep. It is a salvage that someone else repaired so it passed inspection. It has 105K miles on it. Since this is happening in the heat of Arizona summer and only when I get to 35mph to 75mph, I check belts, rollers, hoses, and everything a "non-mechanical minded driver" can think of. It does not happen when I am idling so it is very difficult to diagnose. If it were U-joints, wouldn't that whistle at lower speeds? Also, why would that instantly get louder then quiet then loud when I accelerate? If I keep the accelerator in the same position, it will get quiet then loud again. I'm very perplexed!!

 

[Russell Balzan]

Also check any light bars or other accessories that could be catching wind and causing noise.

The picture I have is the actual jeep. No light bars or other accessories yet. I would agree with you if it were constant whistling. But the whistling adjusts when I step on the accelerator or take my foot off. I don't think I have enough acceleration or deceleration to affect the noise by speed.

 

[Russell Balzan]

The description sounds like a CAI whistle as @Jake Portillo suggested. Do you have an aftermarket air cleaner assembly?

All stock currently. No aftermarket parts yet.

 

[Russell Balzan]

Vacuum line, I would have guessed too. However, this happened to me but in the deep winter. Was a loose bolt on the pipes (upper cats exhaust)that attached to the manifold. Can very well be the one closest to the engine firewall.


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Whether the HVAC is on or off the whistling persists.

 

[Xposure]

Is it a whistle or more whine? Sometimes gears can whine when you get on and off the gas, turn, speed up, slow down, etc.

 

[Russell Balzan]

Is it a whistle or more whine? Sometimes gears can whine when you get on and off the gas, turn, speed up, slow down, etc.

I guess it could be a whine. To hard to tell if it is metallic or not., What are you thinking? U-joint?

 

[tj2000]

its the 2 back bolts on exhaust manifold close to firewall. they tend to loose up. give a nice tight turn on both. sound will disappear

 

[dbbd1]

A loose clamp or a leak on the air intake somewhere?

 

[broken scope]

Check the 4 bolts on your throttle body. Dont overtighten.

 

[LittleGarage]

Did you ever find the solution? Mine just started doing this. More of a whistle, I will check the back two bolts on the manifold.

 

[LittleGarage]

Replaced my belt tensioner and the sound went away so far... two bolts on manifold were tight.