I play on a low spec laptop (I'm one of those 30 to 20 frame rate bois). This might be part of the problem. But the sentinels do not vibrate in resource takeover though.
Low specs ftw 
Hmm, I'm not sure, I believe it's probably just a mission glitch, in the training and the Mission: EMP. But it very well could be of the specs from you're laptop. I don't believe it is game changing. But I'm not sure.
In my video im currently working on, I do recommend using the Escort Drone. It is very useful when trying to kill the sentinels that spawn so frequently. You might want to run the perks, Fast Reload, Marathon, and Drone Helper (I believe that's what it's called).
The reloading perk helps when you need to kill those pesky crawlers, and clear waves of sentinels. The marathon perk helps you get to the EMP faster, so you don't run out of time, and the Drone Helper helps by reducing the amount needed to put the Escort Drone up by 100 points. If you do have the AR57 unlocked, I find it suitable, although the K2C and the MP5 you get at the start of the game works just as well.
More explanation is coming in my video, including the best routes to take and how to do it in the fastest time. 