Rear-end howl @70mph (video)

[Live Wire]

Hello all,

Looking for a little help in troubleshooting a rear end noise that, up to this point, has not caused any issues but is annoying.

I don't know how best to describe it other than a howling sound and really reaches it's peak around 70mph from a loudness perspective. I occurs in 4th, 5th, and 6th gear, but suspect it's there in whatever gear you use to get to 70.

There is no change in sound when engaging the clutch. It drones in the cabin so it's tough to pinpoint exact location while driving, but I'm pretty confident its coming from the rear of the car. Given the sound it makes when you let off the gas at 75-80, I don't think it's wheel hubs or bearings. It's been there as long as I've had the car which is a little over a year but I wouldn't mind getting it taken care of.

I posted a quick video I took in car. It's a convertible and it's 70mph+ so lots of road noise, but you'll get the idea. When you see the deceleration in the video, that's me taking foot off the gas, nothing else. You'll hear what i meant above in the sound change.

I'm the fourth owner, so I don't have a complete inventory of all mods so I don't know if the gears have ever been swapped. Is this a common sound from 3.73 or 4.10s?

As always, any input is appreciated!

2003 Cobra rear end howl - YouTube

 

[Live Wire]

I don't know why I didn't put this together until now, but I was doing a search in the Driveline section for just "70mph" and came across someone asking what gear ratio they have because their GPS said they were going slower than what the speedo says. Ironically enough, recently I went past one of those portable radar trailer things the cops place around town to tell you how fast you're going and I noticed that my speedo said 50 and the radar said 47. I'm betting there are different gears in there.

 

[01cobravortech]

After I had the the rubber differential bushings replaced with aluminim, I started getting a howl that starts at about 70mph and gets louder. Not sure if this is the source of yours, but I'd take a look to see what bushings you have holding your diff together. I kind of have grown to like the howl. lol

 

[MBoyle1]

mine starting doing when I installed aluminum diff. bushings.Right around 70 MPH is when it starts to get loud.

 

[DT_C03RA]

If you're in 6th gear doing around 2k rpms at 70mph, then I'm pretty sure you have stock 3.55's still.

 

[Live Wire]

If you're in 6th gear doing around 2k rpms at 70mph, then I'm pretty sure you have stock 3.55's still.

Keep in mind, I don't think I am actually doing 70mph. Based on my recent experience with the mobile radar machine, I was doing 50 on the speedometer, but only 47 on the radar. I know the radar is right, because I went by it in my truck with the speed control set to 50 and the radar showed 50. In my video, it shows me going 70, but I bet I am more in the 65-66mph range.

Going to do some more tests with a GPS. I got some baselines from another post of what RPMs you should see at 60mph with 3.73 gears.

I guess my original question still stands regarding aftermarket gears... is this rear-end howl common?

 

[DT_C03RA]

I see what you're saying, but my point is the rpms should be higher at 70 mph with a lower gear (higher numerically). I know in mine at 2k rpms I'm right around 70 mph. IDK, I'm not the expert on this, but this is what would make the most sense to me. It's also hard to tell exactly what rpm it's at in the video, but it gives pretty good idea. If you had 3.73's in there I would guess the rpms at 70 wouldn't be that much of a difference though, so it is a possibility.

Hopefully the GPS gives you some good data.

As far as the howl, I couldn't say since I've never changed mine out on this car. Anytime you mess with the rear end on any car from my experience you can run into issues if things aren't set up correctly. I would look underneath and see if you have different bushings like noted in other posts. I know most see NVH go up on these cars once they change out the stock rubber bushings for Delrin or other types.

If that was done on the car then that could definitely explain a lot. It's pretty hard to give anyone a great diagnostics based on a video, but at least it gives you things to look at and a direction. If you're really concerned somethings wrong, I'd just take it to your most trusted mechanic and see what they think after a ride along.

 

[rattle_snake]

I guess my original question still stands regarding aftermarket gears... is this rear-end howl common?

Mine is horrible. REALLY LOUD after solid bushings. unacceptable. sucks. Wife even OK'd paying to fix it which would be new gear set and install cost, which i really saying something 'cause she doesn't want me to spend another penny on it, ever.

 

[NJredfire03]

Damn, I'm about to do the aluminum front diff mount bushings. If it's normal and then it is what it is. OP good luck with your research

 

[Dikger]

rear end howl

I completely feel your pain. Mine has had a vibration and low end rumble that reverbarates throughout the whole car, ever since i changed the gears out to 373's. The sound usally starts between 80-85 and doesn't go away if you push in the clutch. I explained all of this to the speedshop that did the gear install, but noone will go with me for a ride to demonstrate the problem. Makes me wonder if they didn't do the proper gauging on the gears. It also makes noise at other times. Sounds like a little whinning at cruising speeds between 40-60. Please let me know what you find out.

 

[WhiTriCobra]

Mine did the same and after a gear swap, it went away. A howl could be from a gear swap and they didn't set the backlash correctly.

 

[Ukfox89]

I just switched to MM diff bushings and I have noticed a howl at 60mph or so. Very light noise and my abs light keeps coming on and off. Very annoying.