High pitched tone from car

[Drowner 10+ year member]

I'm in the middle of deadening a 2004 Hyundai Accent. I'm doing it over a few weeks so I've been driving the car w/out the interior in it. (The comments I'm getting when I use a drive through are priceless! "Oh dam... I thought you had an oven back there with all of that foil!" //content.invisioncic.com/y282845/emoticons/wow.gif.23d729408e9177caa2a0ed6a2ba6588e.gif )

Anyway, after I took the back seat and trunk panels out of the car I started hearing a very high pitch tone. I can't tell where it is comming from except that it's towards the trunk.

I thought it might be the exhaust but the only time I can get the pitch to change is when I cause a voltage drop (by rolling the windows up and down). I think this rules out anything to do with the engine. So that leaves electrical or maybe the fuel pump? Any ideas on how to track this thing down? :stuck:

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[boister77 10+ year member]

is it coming from your speakers? are you using external amps?

 

[Drowner 10+ year member]

Nope. No stereo, no interior. This sound is comming from the car itself. It sounds like a bad capacitor in a monitor/dumb terminal/CRT. Very high pitch and hard to localize. I'm almost positive it's electrical but I can't imagine what would be in the back of the car that could generate such a tone.

 

[OLD_SCHOOL 10+ year member]

holly crap exact samething is happening to me mine does it at 45-50 mph i have duel exaust out the rear with big chrome tips i blame on it. i jerked the rear seats and stuff i started hearing it the tone is about 200 hz i have dodge dakota quad cab 2003

 

[jellyfish420 10+ year member]

when your driving or when your sitting still?

 

[Drowner 10+ year member]

Both driving and sitting still. There is no change in the tone when I hit the gas. It only changes when I cause a voltage drop by turning the AC on or putting the windows up/down. The frequency drops for a second and then goes right back.

 

[jellyfish420 10+ year member]

??? i don't know. i was gonna say tires cause sometimes tires can hum. but not if its sitting still.

 

[jellyfish420 10+ year member]

have you climbed under the car while it was running to see if you can pinpoint its location?

if i had to guess id guess it might be the fuel pump. some whine louder that others. go out to the car, make sure everything is shut off(radio, a/c) so its quiet then turn the key to acc. if it makes that hum noise for a sec, then stops, then its your fuel pump. you should hear your fuel pump pressurize the system when you turn it to acc.

 

[Depression 10+ year member]

That is Weird..I have a feeling it's something related to the Fuel pump or something in that aspect...Try sitting in the car before starting it..Turn the key "just" to get power but do not turn the car engine on..If you here this sound with the Engine off but electical going through the system..It is probably the fuel pump..This may be a sound that always existed but is "more" apparent because the whole interior is out. I have a feeling it will dissappear when everything is installed again..Otherwise you may have "moved" something while deadening the inside and caused some sort of malfunction in any electrical stuff in the back?

SORRY JELLYFISH...I didn't see your post come up and you are saying exactly what I AM!!!LOL

 

[Drowner 10+ year member]

That's too funny //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Ok, I'll try that next. The one thing I'm not sure I made clear is that this noise is a very high frequency. I'd say around 15-20 khz. It's not like the hum of a tire on the highway.

Thanks for your help guys! I'll post back in a few hours and share my findings...

 

[Depression 10+ year member]

High pitched to me means it's gotta be an electrical whine....Some chevy trucks around 96-98 have this sound all the time while running. you can hear it just driving next to them on the street.I hate it!

 

[Drowner 10+ year member]

Yeah I hear ya, but what could be doing that in the back half of the car? Maybe it's a vacuum leak? Hmm...

 

[deadboi77 10+ year member]

you could get one of those auto stethascopes(sp)like doctors use but for autos..i bought one a couple days ago cuz i had to pin point where a knockin in the engine was coming from and its either the main bearings or piston bearing either way there gettin fixed later tonight

 

[jellyfish420 10+ year member]

That's too funny //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
Ok, I'll try that next. The one thing I'm not sure I made clear is that this noise is a very high frequency. I'd say around 15-20 khz. It's not like the hum of a tire on the highway.

Thanks for your help guys! I'll post back in a few hours and share my findings...

someone said 200Hz thats what made me think tires. but 15-20kHz. fuel pump, definately! once you finish deadening and put the interior bad in. it should be gone.

 

[Depression 10+ year member]

I AGREE..I know it sounds stupid to go ahead an re-install everything without fixing that sound..I will bet that re-installing will cause that high pitch to "magically" disappear

It's The Fuel Pump...You just couldn't hear it before!!