I just installed my stereo in my new vehicle (previous vehicle was in accident) and i am having the same problem in this vehicle as the last. I get an extremly loud squeel coming from the speakers when vehicle is started, it gets louder when put in gear (both vehicles are standard), accelerates, or even stepping on brake. I have tried everything to fix this problem. I have made sure power wire and rca's are opposite sides, everything is grounded PROPERLY, the noise got really loud after adding the second amp, but i tried two completly different amps and still the same noise. I have installed noise reducers and it didnt help. I tried switching decks. I disconnected the car wiring to the deck and replaced with my own wire straight to fuse box and straight to battery. I tried seperate grounds, ground blocks, about 8 pairs of rca's. My ground wires are same size as power wire. I have looked on the net numerious times and everything leads to ground loop, rca's not good enough quality, ect. but i have tried all the things they say to fix the problem; yet it never seems to fix my problem If anyone can help me with this it would be greatly appreciated and i would owe you big time I DONT KNOW WHAT ELSE TO DO PLEASE HELP

 

1- have you tried grounded the outer run of the RCA that works for some setups that lost that (I do not think this is your problem)
2- if a speaker output (in this case the speaker itself) is grounded you will have the symptoms you describe
3- It sounds like you have tried everything I recommend doing a logical progression of trouble shooting. It is a bit of a 'do over' but this beats pulling your hair out. start with something that works and just add components till the problem starts, change only ONE thing at a time.
do things like:
power the speakers from the HU only...

replace the HU with a portable CD player (you will need a 1/4" jack to RCA cable) this will tell if the HU is the source or not

read the instructions if all else fails

I remember a band from the late 70's called Chilliwack