buzzing sound when running

[hey...it runs]

Hey guys. I have an 89 n/a 5 speed with a completely after market stereo. When the car is in accessory mode the stereo sounds perfect. However, when the car is running there is a faint humming noise. When you rev it it matches the pitch of the engine rpms. It is the same volume no matter what the head unit is set on. When you play music it is still there but just overpowered.

I believe it is some type of short but I'm not sure where to look. I have two amps, one for speakers and one for the sub running off of three sets of RCA cables. The humm is played through the front and rear speaker which leads me to believe its not a short in the cables. The head unit is grounded to the chassis. The amps are as well. If you mess with the mounting screws (into the matal backside of the rear seats) there will be static of for a second but I don't believe they are shorting as I messed with them the other day and could not get the noise to dissapear. It only got worse or better.
Could the factory ground be too weak on the battery (I'm running a 4g power wire to the amps)? Could it be the amp mounting even though I tried messing with it? Or could it be the wiring on the head unit? Thanks for your help guys.

(The head unit uses the factory power supply, but is not hooked up to speakers. It is used for the RCA signal and it is grounded to the metal bracket nearby.)

 

[te72]

Try an additional ground for the head unit. We had to do something like this to my 88 that I had, got rid of the problem. My 89 currently does this "buzzing" you speak of, but I don't mind so much anymore, sounds like a supercharger.

 

[hey...it runs]

Lol mine almost sounds like a Turbo. But thank you! I will try that and let you know probably tomorrow on this thread.

 

[sharpsupra]

if the screws you mounted the amps are directly to the chassis then that will give you a ground loop. isolate the amp heatsink from the chassis.

 

[hey...it runs]

Sorry it's been so long. I think it may be those screws. I tried touching a wore to a metal ground and the outside of my head unit and it had no affect. I would just assume it's those screws except it seems to get worse and better from day to day. Like I said, I did mess with the screws a little before. I probably would have played with the mounting last weekend but it was cold and I had stuff to do. I've read that some people ground their headunit to the frame and some people use the stock wiring ground. Apparently some cars buzz on one of the two but not the other. Does anyone here have experience with grounding to the chassis like I'm doing? When I get to it ill try messing with the screws. If that doesn't work maybe switch grounds on the deck or should mine be fine?thanks!

 

[mecevans]

Low resistance spark plug wires can do this.

 

[hey...it runs]

Interesting you say that because my car only has the single conductor plugs instead of the double tipped ones. One of the plug wires got a little frayed from a small animal? But it's not shorting. I believe the plug wires are around 15 years old as well.

 

[te72]

Low resistance spark plug wires can do this.

I can see that, it is electrical interference from the alternator causing this noise, correct? However, in my case, I am running a COP setup, no spark plug wires to be found...

 

[3p141592654]

Put a line filter on the 12V feeds to the equipment. This is not a ground loop, its alternator rectifier noise getting in to your equipment.

 

[te72]

Thanks 3p, will do that when swapping shells.

 

[3p141592654]

Also make sure the filters that Toyota put on the car are still there.

 

[hey...it runs]

Took a while but I re-mounted the amp isolated from the chassis. Cut out about 50% of the ground loop but it's still there a little. My friend gave me a 2ga. Battery terminal and I'm thinking of replacing the stock on with it. I was looking at it today and what is it? 10ga? It's tiny. I'm thinking replacing that might eliminate a little more of it. I don't want to spend money on a filter unless I have to but it's good to know that might fix it. So far so good. Thanks guys. Sorry for the late reply but it's been cold and I've been busy. Today I felt like working on her though.

 

[hey...it runs]

Just another update. While I was swapping batteries I replaced the stock ground terminal with a 2ga one a friend gave me. Buzzing is almost completely gone! Thinking that ill do the engine to chassis ground 2 GA as well. The stock alternator to positive wiring should be fine as is right?

 

[dontbskurd]

From my experience messing with car audios back in the days, more like 10-15 years. Try shortening the black ground wire from the amp to the chassis. Basically wherever there is a ground wire keep it as short as possible. Judging that you have 2 amps, there is a power splitter involved. Chassis to splitter ground wire needs to be short. I recommend 5 inches or less depending on mounting locations. And then from splitter to amps as short as possible with the ground wires. I recommend using quality wires, but its up to the person. Give that a try and let me know how it goes. It worked wonders for me back then.

 

[hey...it runs]

I actually recently got a duralast gold battery and upgraded the ground terminal from the battery to the chassis to 4 GA. To match the wire on my power dist. Blocks. I'm running Rockford fosgate four gauge to the splits (about three feet). Only the sub amp and power cap are grounded in the block and the speaker amp is grounded seperately with about 1-1.5 feet of 8 gauge which is ground to the same place my ground block is grounded to. The negative terminal upgrade and duralast gold worked wonders for the problem. Its almost completely gone now. I also should mention it is an 800CCA battery as was the last one, but I don't think the last one was making nearly that much power. Thanks for the help here guys!