msce85

Situation:
I had a new Interstate-MegatronPlus battery installed in my 1988-928S4 today at the Interstate Battery dealer. The car started right up with both the A/C & radio on. I then took off for home. (I note that the battery was last replaced 5 years ago-same battery & dealer, no problems).
Problem:
Once I arrived home and turned the A/C & radio off I heard a faint buzzing (or high pitched humming) coming from the back of the car with the engine still running. I then looked in the battery compartment and the noise seemed to be coming from the battery, or under it. When I looked under the rear of the car the noise was more perceptible. All I could see was the gas tank and rear axle. I turned the ignition off and the buzzing noise immediately ceased also. When I turned the car on again the buzzing noise immediately started again. I then drove back to the dealer (about 11 miles, mostly interstate). The car started and ran great as usual. Once, when I gunned the accelerator, the buzz noise ceased for awhile; however, it resumed soon again and remained constant regardless of acceleration or deceleration. The dash board voltage meter stayed just above 12V all the way back with the A/C & radio on except when I stopped at a red light where it then dropped just below 12V until I started moving again. Once back at Interstate I noted the buzzing noise to the dealer. He commented that a battery does not make a noise, but stated that the buzzing seemed to be coming from under the rear of the car. He checked the voltage of the battery at 13.3V with the car running. The ignition was then turned off, the ground cable was disconnected and the battery tested at 12.2V. The ground cable was reconnected and the car started right up and ran great as usual, but the buzzing/humming noise started immediately again and remained all the way back home.
Question:
What is this buzzing/humming noise that was never there before I had the battery replaced today?
Thanks for any insight or thoughts,
Michael

Speedtoys

Fuel pump.

They're important.

linderpat

^^^What he said. Fuel pump. They get lubricated by the gas in the tank, and don't like it when levels get too low, for extended periods of time. If the buzzing continues after at least a half full tank, then the pump may be on its last legs. Also check the fuel pump fuse at the CE panel in the passenger footwell. See if there are burn marks on it. A pump going bad will cause that fuse to overheat, but not necessarily blow.

SeanR

This is exactly how a person should post an issue or question. He posted his issue, he had thoughts and he has his car in his signature. That's how ya do it.

And as far as the issue, already been answered I just wanted to give you cudo's for a properly thought out post.

msce85

Thanks everyone for taking the time to read my post and your comments/replies. I knew it was likely the fuel pump, but "wisdom in consultation". Thanks guys!

mark kibort

I had a loud buzzer for a few years..it just never died.

Tom in Austin

My pump buzz was most noticeable before pulling out of the garage in the morning. Interesting question how long it will work once the buzzing has started ... I went ahead and replaced it.

James Bailey

question becomes where will you be WHEN it finally does lock up ???

mark kibort

that is the $179 dollar question!

James Bailey

no is a $179 solution....how much does it cost if you are 200 miles from home on a dark and stormy night ? or if it fails during qualifying for a race where you have paid all the entry fees and driven to get there ? those are the questions

mark kibort

I meant, fix it... $179 is cheap compared to the costs of what could happen! takes about 30 to 60min to swap out, and then you dont have to worry about it.