High pitch tone

[Mikeym87]

Iv had an ongoing problem with my car for the last few months now. Audi A3 8P with MMI/ RNSE and BOSE


When the car is not running everything is spot on with the sound system


However, when i start the engine i get an intermittent high pitch tone (Varies in loudness, length and interval between the noise) also it does not increase/ decrease dependant on RPM, the car can be idling and the noise is there or cruising down road.


What i have checked:


All ground connections within HU, Amp, battery, alternator etc. Battery condition is good and alternator works fine.


The car had an aftermarket ipod lead fitted before i bought, i have disconnected this to check if noise was from here but still no fix. This was the only none standard component within car.


Beginning to pull my hair out with it, unsure if the fault is with the amp or HU?(have checked for any usual water damage from rear window wash hose but all is ok)


Just looking for any more ideas what to check or if anyone has had a similar problem?


Thanks in advance


Mikey

 

[Mart77]

Earth track on the amp or HU would be my first guess ( althought normally gets worse with rpm ) , could also be a speaker shorting out try disconnecting 1 speaker at a time.

 

[Mikeym87]

Cheers Mart, will give that a go tomorrow. I had another wee go at it today....when i unplug the speaker out block at the back of the HU the noise get louder and constant.

Ruled out the radio antenna amplifiers in the rear window being the cause. Disconnected these and the intermittent noise is still there. Does the sub have its own amp? If so would this be worth checking?

 

[Mart77]

Should be all in one amp in the rear quarter