Riz

Hey all! New here and not so car savvy. I have a question that I still haven't quite found the answer to while checking out some auto forums. I've got a 97' 3.8L pony nearing about 175,000 miles. I've been having an electrical sounding hum coming from it's back end ever since I've had to get the battery and alternator replaced about 2 months ago. It's just now getting more noticeable. I can hear the noise inside and out of the car. It also changes pitch when the blinker is on? Such as in it goes with the blinker clicking instead of one continuous hum I'd normally hear. It doesn't get louder or quieter while driving or in idle either. I'm really hoping it isn't the fuel pump, but it's in that general area I believe... I haven't had any leaks or weird smells, but I'm not sure what I'd be looking for exactly if it is. I am planning on getting this fixed hopefully in the next few weeks, but I would really like to hear what you guys think it could possibly be! Thank you!

Riz

Adding some info from this morning. I notice the higher the voltmeter is reading, the louder the hum. Also I can drain the voltmeter down a bit by just the automatic window button. Ever since I got a new batt. the voltmeter does read really close to the 18 side, but still in normal. I can hear the hum drop down when the voltmeter drops too? Almost sounds like my car wants to shut off when it does drop out of the blue. If it was the battery, wouldn't I hear it from the battery and not the middle rear of my car? Hm.

Daehawk

No idea why it's coming from the back end. Really the only electrical other than light I can think of back there is fuel pump and defroster.

If it only started with the new battery and alternator Id look at the alternator. Did you get a much bigger one or a smaller one? Was it a rebuilt or used? Actually Im not sure you can buy a brand new one these days anyways.

mbeer

Check your fuel pressure when the hum is high pitched, then check again when it's low pitched and see if it is different.
I believe you can "borrow" a fuel pressure gauge from advance auto. They just require a deposit for it.

Riz

Thanks for the responses! I've had to go through 2 alternators in the past..5 months? First time it just time to replace it and going bad, and the 2nd time was because the battery burnt out the alternator by a bad battery cell. Luckily, the same guy I went to for the first alternator replaced it for free since it was only a few months since I got the new one. I was under the assumption it was new since he didn't say otherwise, but like you said, I think you can only get them remanufactured... It seems to be the same size as the last one. Maybe bigger than the first alternator that went bad though? Can't say for sure.

And thank you for the idea of the fuel pressure gauge idea. I have a co-worker buddy who is luckily a former mechanic and I think he said he had one when I asked about after seeing this suggestion. I've asked him about my issue, and he said the same thing as Daehawk about the only thing really electrical back there is the fuel pump and light. He's thinking it may be a bad ground from the battery or alternator. Going to check the fuel pressure anyway though just encase. May be some time before out schedules work out to check out the noise, but I'm curious of what it is. I'll update once we find out...

petrock

If it is a convertible, then there is a motor/pump thing to raise and lower the top behind the rear seat. I think there are also some speakers too on coupes (but I could be wrong).


That is what I was thinking and the hum is coming from your sound system.

Tipsy Bojangles

I have a 96 Gt vert and get the same noise.. it isn't the speakers because the rear speakers were out when I bought the car. It really made me feel ghetto when I first heard it from outside the car :/ My best guess is fuel pump, but I don't know if it's going out or if the prev owner misplaced some sound deadening. The car runs great, but it is something that bugs me. I'd like to know what you come up with. Amps are a possibility too, I have the mach 460 system, I don't know what your car is equipped with. However I know for a fact there's a bad ground in my car somewhere, as I get a speaker pop on startup and maybe unrelated but the pass window only rolls from my controls. Hope you find it, I've been turning up the stereo to make myself forget about it

Georgi

So was you able to figure out what the dam humming noise is coming from.