I have a USB sound card for an Android Tablet which is connected to a Aux input in my car radio. Works good, however when I put the tablet to sleep as the tablet is going to sleep, the sound card generates a high pitch screaching sound for about 5 seconds or so before the tablet has slept and put the USB devices to sleep and then the noise stops. One way to solve this is for me to put a relay and cut the +5v power line on the USB device and have it power off and on instantly. Is there any other solution to this? any ideas why this could be happening?

Thanks

 

Ok, so I've determined the sound is coming because my usb sound card is connected to a +12v powered USB hub. When I turn ignition off the power to the usb hub turns off and it initiates a suspend tablet process where the tablet goes to sleep. During this process because the Hub doesn't have power but the tablet has power it creates some kind of noise back. One way to solve it is to power the usb hub on permanent power.

 

What else is connected to the hub? Do you really need the hub?

 

What else is connected to the hub? Do you really need the hub?

The hub has a reverse camera and a Apple carplay dongle. So total of 3 devices including the soundcard.

 

Probably leaving the hub powered would be the simple choice, or switching it off after the radio is switched off might solve the noise problem.