Ground loops in phones in cars

[kfitch42]

BACKGROUND: I recently had a problem with my Nexus 5X phone rebooting periodically. The problem developed slowly over a month or so, starting with a random reboot every few days, but eventually it was more like every 30ish minutes. I tried all the software things (e.g. factory reset), but nothing helped. It was still under warranty (about 6 months old), and Google sent me a replacement which is not experiencing the reboot problem.

I have been pondering if there was something I did that might have precipitated the problems. (NOTE: It never experience a severe drop or got wet)

Nearly every day I plug it into a car charger and the AUX jack in my car. If I plug in the AUX first, I will notice a hiss/hum start as soon as I plug in the charger. I am guessing this is a symptom of some kind of ground loop. The curious thing is that the hiss/hum goes away as soon as I start to play any audio, even if that audio is completely silent ( one podcast I listen to tends to start with a second or two of silence).

So, is it likely I inadvertently damaged my phone, or is it more likely the phone had a defect that took time to manifest?

[Monkeh]

There may be a ground loop, but that hiss is actually the noise of a floating input. Your phone will not be driving the output until an application opens it.

[djkoell]

I resolved the same issue in my car by picking up an $8 [amazonsearch]ground loop isolator[/amazonsearch] from amazon. 

[sparx]

Same issue when trying to get my tablet and amplifier working - playing sounds was fine, but when no sound or application driving the headphone output it would always pick up random noise and consequently amplify it...

[zapta]

I resolved the same issue in my car by picking up an $8 [amazonsearch]ground loop isolator[/amazonsearch] from amazon.

Same here, this one  https://www.amazon.com/gp/product/B004E8YRS0 . It solved the noise problem of my BT adapter which is plugged into a cigarette lighter socket and into the aux input of the audio system.