I went over a speed bump today, it has started making a loud noise, I almost thought I was dragging something on the road but cannot see anything, it's particularly noisy when I am driving slowly, its coming from the rear, under the truck bed, I can still accelerate and brake
My car has 149000 miles.
My car has an automatic transmission.
It sounds like one of your leaf spring shackles has broken. It is very common for them to get rusty and break.
The noise you are hearing is probably the shackle running on the underside of the bed. Go to the back of the truck and it should be pretty easy to see at the back end of one of the springs.
I would ask for help from one of the mechanics at YourMechanic to inspect the noise, and replace the broken shackle, if that is the cause.