Ok, I was driving my 05 GT today and I noticed a noise while I had my radio off, it was actually pretty loud and my gf heard it too. Basically what is going on is when I am going between 43-47 mph I get a humming noise that fades in and out, any slower or faster and it disappears. I heard it and my gf actually thought my alarm was going off because it was pretty loud and faded in and out, but it wasn't my alarm obviously. Any ideas on what it could be? I thought exhaust, but it only happens at a certain speed, not a certain rpm, so I am kinda stumped. Mods are intake, tune, gears, and full exhaust, headers back, and I know it isn't the gears as they have been in for a while now.
Thanks for any help,
Bill

 

It's hard to say without hearing the sound, but do you think it might be a wheel out of balance? Maybe one of the weights fell off. The fact that its speed sensitive and not RPM sensitive would indicate something with your wheels/tires. Does it do it all the time on any road at that speed?

 

You know I was thinking that too, I'll check into that. I've gotten it to do it on any road so far, not just one specific one.

 

Thats good in its own way, consistency will help in diagnosis. I know you said that it didnt seem RPM sensitive, but have you tried going that speed in a different gear (provided you have a manual)?

 

No I have not, I will try to narrow it down more tomorrow, and I do have a standard so I can just hang it in 3rd or 4th at 45.

 

That should be a better way of eliminating the RPM factor. I'm Looking forward to hear your results.

 

Ok I'll give it a try and report back tomorrow.

 

Wow, couple weeks back I searched all the forums for just this same issue and found nothing. I have, I think, the same sound....it is a humming sound that fades in and out. The "alternating" hum is very steady and doesn't seem to speed up or slow down. It cycles in and out rather slowly, like it hums for about a second then fades out, then fades back in and so on....... I don't think it's a tire, because at that speed, the wheel is turning at about 9revs/sec (9Hz) and that doesn't seem to match the fading in and out cycle of the hum?
I started thinking it had to be something with the air flow and resonance, either the intake or the exhaust? I really have no idea? I do not remember hearing it before adding some mods to my car and since I added them all around the same time, I can't pinpoint the cause. Here's what I upgraded (I have a v6): FRPP CAI & tune, 8.8 rear axle with stock 3.55 gears, CHE LCA's, Roush rear springs, and 4in Shaftmasters AL driveshaft. I already had
a FRPP dual exhaust w/x-pipe.

I am very interested in what you find out as well as if anyone else has this issue or any input. Keep us posted.

 

Driving on the highway, I have a similar sinuous humming that seems to match up with 1-second intervals. I'm going 65-70 on the highway with the throttle lightly pressed and moving at constant speed. I figure it's resonance from my O/R exhaust and does not go away unless I accelerate or decelerate.

I don't think much of it. Either the windows are down, I'm listening to music, or it's nice white noise for doing some good ol' thinkin'.

 

Back in 2008 I had a V6 pony car. I put an X pipe on it converting to duals and I used GT manual tranny axle backs. I had simular noises. I cut the vibration dampners off the V6 exhaust (metal brackets with rubber weights) and welded them on to the new tailpipes right after they came over the axle, just before the mufflers. That got rid of most of my resonance. The V6 cars are the only ones that have these vibration dampeners I beleive. You could fab some of your own, I think if you were to weld a rod with a weight off your pipes somehwere between the crossover (H or X) and the mufflers, you might get the same results. Just an idea based off my experience. Good Luck!
Jim