sometimes when i ride along the country or after i killed some enemys my gamepad starts to shake, i look around with my witcher senses but i cant find anything... so why does it shake?

It's Geralt's amulet. There should be something nearby. Can be a lot of things.

meh, i use witcher senses but cant find anything

You should be able to turn that off in the Options, if it bothers you. Control Settings / Vibration

i rather want to know what to look for

I have the same issue. Some glitch in the area I guess.
It reminds me of Gamebryo (Oblivion+Skyrim engine) where kicking clutter bones would cause damage. I guess it is something similar. It looks too random to be a hidden secret.

If you have Quen active, whenever it deactivates itself, the gamepad will rumble. Even knowing this, I still look for trouble every time it does so.

hmm that may be it, i will pay more attention to it in the future