Tone heard when starting car
 

Hello all. Recently I have noticed a "tone noise" coming from the rear of the underside of the car when I start it. Never noticed it before until recently. That is the only time I hear that tone and it only lasts as long as the fuel pump runs, then stops.


I think it might be the battery lost some of its juice as I have an amp installed in the back with a capacitor and a digital read out display on it. Running I get a read out of 13.7 volts. Off about 12.8 volts. Battery is fairly new not more than three years old.


Car runs and drives perfect otherwise, just curious about that tone I am hearing.
Any suggestions or thoughts perhaps?

It's basically impossible to diagnose "weird noises" over the internet. What one person might call a "tone noise", another might call a "buzz" or a "hum" or some other essentially meaningless description.

You have described it as coming from the rear underneath the car. You are right to acknowledge that the only likely candidates for the source of the noise in that area are the fuel pump and your amp. You might want to disconnect each in turn and see if the noise goes away. Once you have pinned down the source you can decide what, if anything, you want to do about it.