Why? Many folk install apps from other than the Google store and some will make LD calls and texts to make money off your phone. I can't know what you did or installed but any app outside the store is to be removed and maybe the phone factory reset (do you have backups of your stuff?) to toss out possible malware.
My Huawei P20 Pro - new, under 6 months old - has started making odd noises.
It makes the audible sound of dialing out for just a second, despite the fact that I am not making any calls, there being no notifications related to the sound and all my system sounds being muted.
Has anyone come across this before? Is it a sign of something I should be worried about?
Any help would be greatly appreciated.

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