Plug in wire to aux and the engine noise comes thru speakers

Teresa, I went thru the same only to find rodents chewing wires costing me$800 to fix. Hope your situation is different!

CHECK TWO WIRES THAT CONNECT THE SPEAKER [RED AND BLACK] IF THEY HAVE ATTACHED TOGETHER

if the radio and DVD work, and only one channel comes on when you plug in your iPhone (i assume used for music), you may have a mono plug
(the tip looks like two pieces of metal, separated by plastic), going into a "stereo" jack (the stereo plug going into this should look like three pieces of metal, separated by two plastic).
for the earpiece with mike, used on a cell, that plug would look like four pieces of metal.

The aux batteries are usually able to be disconnected from the engine charging system , and main battery....to keep from discharging everything.... Look for a switch...

1998 Chevrolet Malibu Car Stereo Wiring Diagram

Car Radio Battery Constant 12v+ Wire: Orange
Car Radio Accessory Switched 12v+ Wire: Yellow
Car Radio Ground Wire: Black
Car Radio Illumination Wire: Gray
Car Stereo Dimmer Wire: Brown
Car Stereo Antenna Trigger Wire: Pink
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Car Audio Front Speakers Size: 4? x 6?
Car Audio Front Speakers Location: Doors
Left Front Speaker Positive Wire (+): Tan
Left Front Speaker Negative Wire (-): Gray
Right Front Speaker Positive Wire (+): Light Green
Right Front Speaker Negative Wire (-): Dark Green
Car Audio Rear Speakers Size: 6? x 9?
Car Audio Rear Speakers Location: Rear Deck
Left Rear Speaker Positive Wire (+): Brown
Left Rear Speaker Negative Wire (-): Yellow
Right Rear Speaker Positive Wire (+): Dark Blue
Right Rear Speaker Negative Wire (-): Light Blue

Hope this helps (remember to rate this).

The "noise" is coming from the alternator and is being injected into all powered accessories. Some devices are better at filtering than others.

Best way to eliminate the noise in your audio system is to add a low-pass filter (aka choke filter) on the input power wire to the audio system (red wire?). That will "pass" the noise to ground.

Since the whine is in the 800-5000 cycles per minute, like the engine rpm, you will need a low-pass filter around 5000x60 = 30KHz.

A decent car audio shop can install the proper ampere and frequency filter.

I am not sure if the car is petrol or diesol.If its petrol,the noise will be the ignition coming through the stereo.If you had new spark plug cables put on the car recently,that is the problem.The clicking will probably increase in frequency when you rev the engine.To fix.Suppressor type plug leads or a suppressor wired into the ignition system.A good auto electrician will know what is needed.Hope this is the problem and hope it helps

spark plugs been changed ? cheap plugs can cause this. spark plug wires ok? broken spark plug wire can cause this too or one just arcing to ground pass a loose boot raise hood after dark and run motor watch over all wires to see anything noticeable. Dont touch anything while running or things could go bad for you fast... some electric fan motor have a filter bolted to them this could be? does it vary with the engine? or stay one level? if all else fails it might be easyer to pick up a filter and install it in the power cable to your radio?

Check your wiring harness from the radio to the speakers, as well as the wiring to the speakers themselves. If the insulation is gone, sometimes that open wire will cause that noise. Or, the plug off the back of the radio to the speakers could be loose.

hissing soud is from the altenator ( not a big deal ) have a noise reducer installed or have the stereo rewired for it's power wire from a different location. Very common thing that happens by do it your selfers.

As for oil temp I'm not sure what it should be on thatcar but is it oil tem or oil pressure?