Crazy Noise

[1950StangJump$]

Gonna give you guys a shot before I post to Facebook. 2008 GT with T56 Magnum, RST, 4.10 rear gears, Stage 1 Kenne Bell, Kooks headers, high flow cats, VMP Triple Pass, GT500 intercooler pump, Pedders coilovers and numerous BMR suspension components. 23k miles on the odometer.

Today, I noticed a high pitch whine noise coming from outside the car somewhere (definitely not the interior). It was like a high pitched whistle, only it was constant and a higher frequency than a supercharger. I could not isolate to the left or right. Here is what I learned trying to figure it out:

• No change to vehicle performance
• Appeared to only start when the engine and car got hot.
• Doesn't change with engine speed -- I can rev in neutral while coasting and it doesn't change the sound.
• Doesn't change with vehicle speed EXCEPT that it will always stop when I slow to under 5 mph (and to a stop). So, there is no difference in the sound if I'm doing 40 or 20 mph.
• Turning the AC on or off makes no difference
• Doing anything with the transmission doesn't change the sound, i.e. doesn't start or stop at all if I push the clutch in, change gears, put in in neutral, etc.
• I cannot replicate idling or revving in place, which obviously makes it hard to diagnose.
• Doesn't sound like any gear whine I've ever heard -- and the sound does not change with speed at all like a rear gear whine.
• I have a kill switch on the VMP fans, but killing them makes no difference. I didn't try killing the GT500 pump, but I can't believe a noisy pump would get quiet when the car slows to a stop.

I have a PA Performance 215 amp alternator in it, and I know folks have had mixed reviews with those, but I can't see why that would be noisy only when the car is moving and not be RPM dependent. Same thing with a belt. Plus, its a very "constant" sound . . . does go up and down with engine speed, transmission speed, or wheel speed (except to stop when the car comes to a near stop).

Any ideas?

 

[Racer47]

I don't know what it is but you can use your phone to help find it. Tape the phone where you think its coming from. For example, if you think its the fuel pump, remove the rear seat and tape the phone to the hat if you can. Or put a piece of metal on the hat, then the phone on the metal. Press record and do what it takes to make the noise.

 

[1950StangJump$]

Thanks, that's not a bad option . . . just have to figure out where to start. My first thoughts were fuel pump, cooling fan, alternator, or a supercharger bearing. After my original post, I went out yesterday evening and again this morning, and I couldn't replicate it. Makes me wonder if the noise was heat related, and I was unable to make it come back when the ambient temps were too low.

Seems like alternator or supercharger bearing would go up and down with engine speed though. Not sure if anything changes with the fuel pump at idle versus any other time? With any of the above possibilities I list, would slowing to a stop make the noise stop? Makes me think the computer is making some adjustment somewhere at idle that, by happenstance, is negating the sound.

 

[Racer47]

Its a good idea to pull off your supercharger belt once in a while and spin everything by hand to see if they turn easy. Those belts run so damn tight that they are hard on all the bearings, idlers, alt, water pump, etc.

 

[boomer9999]

Maybe I'm off base big time, but I would check the brake pads for wear.

 

[1950StangJump$]

Thanks. Definitely wasn't brakes.

I have been unable to replicate the problem, so I guess I'm in a wait and see mode. Given it goes away at idle, my new theory is fuel pump. I thought the noise was coming from outside the car and not under the backseat, but will have to listen closer if/when it ever comes back.

I'm guessing I was unable to replicate the noise because it only occurred when the car was really hot and, possibly, lower in gas (1/4 tank). If so, that would certainly be consistent with a failing fuel pump.

Hell, it could have been that a piece of debris got in the pump, and it's gone now. Yay for wishful thinking!