vibration without notification

[l3enQ]

I have a problem which occasionally occurs. when I unlock the phone sometimes it vibrates two or three times, shortly whitout showig any notification.  

I have M4 aqua dual E2333 Lollipop.

[_alexdon_ · Accepted solution]

@l3enQ Have you checked if the same occurs in safe mode? Does anything else happen?

[l3enQ]

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@alexdon wrote:

@l3enQ Have you checked if the same occurs in safe mode? Does anything else happen?

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@alexdon I did not try that, because it happens very randomly and I can't wait that long time to check if it will be happened or not!

[_alexdon_]

It might be a 3rd party involved. Does anything else happen besides vibrating?

[l3enQ]

It might be 3rd party apps, but How do I can find which app cause this?

no, there is nothing except vibration

but sometimes a notification with icon of white square comes whitout any sound or vibration. and dissapears in no time!
this is absolutely a 3rd party app. but i can't find it

is there any log for notifications or system events in android? like event log in microsoft windows for PC!

[_alexdon_]

Did you change settings under developer options? 

[l3enQ]

I unlocked the developer options but it is set to the off always.

my phone is in safe mode and in the last two hours nothing was seen like before.

[_alexdon_]

Keep us updated.

[l3enQ]

the phone was in safe in for 6 hours and nothing happened. and when I restarted to normal it happened again after a few hours.

how I can find the app cause this?
if I can't I will backup datas and do reset factory.

[_alexdon_]

You could go to google play and check what you have installed lately, paying attention to the type of apps you find there (task killers, antivirus, battery savers, launchers etc).