High pitched noise

[Rhino3207]

Hello,

I recently bought a 1996 firebird with audio issues. Whenever the head unit is turned on there is a high pitched "mosquito noise" coming from all of the speakers. The sound is there if the engine is on or off. The audio will still play through the noise but it's fairly loud.

There was an aftermarket Sony head unit in the car already but it didn't have Bluetooth so I swapped it to see if that would fix the issue. I installed a Sony dsx-a415bt. Unfortunately the problem still persisted.

I dug into it and found that it has had every speaker replaced by a previous owner. I looks like they wired the whole system in with speaker wire. Everything is hooked up to a kenwood xr 900-5 amp. Good power and ground on the amp and I cleaned up the ground.

I have only ever replaced head units in vehicles before so I'm a little out of my depths here. Is there something else I should be checking for? Is the amp done for? If the amp is done for is there somewhere I can get it repaired instead of replacing it? Any help is appreciated, thanks.

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[Jimi77 Premium Member]

Sounds like a ground loop. You can try unplugging the RCAs from the HU and see if the whine goes away.

 

[Rhino3207]

I tried that and nothing changed unfortunately. Any other ideas or things to check?

 

[RobGMN Premium Member]

If it's coming directly from the amp, maybe a failing power supply?

 

[Rhino3207]

The noise itself is definitely from the speakers but my thinking is that it could be something wrong with the amp as the root cause.

Im playing with the amp to see if anything happens. Whenever I flip the Hpf filter the noise briefly goes away but that might just be a function of the switch. None of the knobs on the amp seem to impact the noise.

Also I may have been wrong about music still playing through all of the speakers. I think the sub and the front speakers are the only ones working right now. The other ones just broadcast the hight pitched noise

 

[RobGMN Premium Member]

The noise itself is definitely from the speakers but my thinking is that it could be something wrong with the amp as the root cause.

Im playing with the amp to see if anything happens. Whenever I flip the Hpf filter the noise briefly goes away but that might just be a function of the switch. None of the knobs on the amp seem to impact the noise.

Also I may have been wrong about music still playing through all of the speakers. I think the sub and the front speakers are the only ones working right now. The other ones just broadcast the hight pitched noise

If it continued after you disconnected the head unit, you isolated the amp as the problem (assuming no other hardware is in the chain).
I was thinking maybe a failing power supply causing electrical noise, not making noise itself.

How much trouble would it be to pull the amp and isolate it to see if the same is happening outside of the car?

 

[Jimi77 Premium Member]

Stupid forum didn't tell me you replied. Try another source into the RCAs such as you phone.

https://www.monoprice.com/product?p_id=665&srsltid=AfmBOoqLDuXhmvbHIEN-fAe5mED8HWJ2cM1IMPYdubUmGEUzxMiykjZ1

 

[Buck 5,000+ posts]

Does it still make the noise if you unplug the RCA's from the speaker amp?

 

[Deiimos]

As already suggested, with all the rca cables unplugged from the amp, if it still makes the noise, it’s something with the amp. Try unhooking the speakers one at a time at the amp (both positive and negative wires), and see if the noise goes away. Pinched / grounded speaker wires can cause odd problems, and you said they ran new speaker wire. Unlikely an issue here, but it is free to test. Other than this, take the amp out and bench test it out of the vehicle.