I am all of the sudden hearing a loud noise under the hood of my car.

[Sometimes1needhelp2]

This happens at higher rates of speeds such as 55 and higher and most times it does not even happen this happens at random times on the passenger side of my 2013 Ford Fiesta and this sound does not happen anywhere else under the hood of my car always the passenger side and it happens at random times it is smacking against the hood of my car I was thinking it could be the transmission fluid container I believe the only part under my that is loose enough is my transmission fluid container it clips down on 1 side and the other side is completely loose.

 

[Sometimes1needhelp2]

 

[scotman]

That is the coolant reservoir. If you are not certain of its age, get a new one! When they burst it is an immediate disaster in process.
The knocking on that side is much more likely to be the sway bar end link.

 

[Handy Andy]

OR you have a bad strut mount on the Passenger side - if the clunk BANG or rattle occurs on rough roads - the strut mount needs to be replaced -

MOTORCRAFT number AD-1141

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More than likely you hit a bump. This forces the strut up and down really fast and if too hard or sudden (like bottoming out) you may have dislodged the black rubberized insert in the Strut mount. The black insert in the metal bracket above the lower cup that pivots under this mount - holds and allow the strut and tire to rotate on its axis and steer the car.