Pygame Screen breaks when moving line across screen

I am trying to move this image:

On my PyGame screen, right to left and back again. However, as the image moves, every second or so, I get screen tearing flickering, making its way like this:

The code I'm using is a loop like this:

screen.blit(img, (x,y))
pygame.update((x,y),(w,h))
pygame.draw.rect(screen,(0,0,0),((x,y),(w,h)))

      

        
        
        
      

    

So far I have tried to solve the following problem:

Using flags HWSURFACE

, FULLSCREEN

, DOUBLEBUF

when you create a screen, it is not affected, I also adjusted my .update(rect)

on .flip()

(as it is recommended for use DOUBLEBUF

?)

Sharing memory between GPU and CPU (I'm running this on a raspberry pi 2), I tried to give both more memory and no change.

Setting clock.tick to throttle the refresh rate to 60 FPS (higher and lower), this ironed out some of the tearing, but not all

Adjusting the size of each increment to the left or right, making smaller increments, results in less tearing, but also less speed. (Can't be too slow)

Blitting a new black surface instead of drawing a black rectangle over the previous position (while moving the image to make sure there is no trace behind it) when I read somewhere, which is blit

better supported HWSURFACE

than painting, although I can't confirm it? - It had no effect

If anyone has other solutions that can improve the situation, I would be grateful.

I would rather not switch from PyGame to anything else (like pyglet) as I've used quite a few PyGame implementations so far, but I'm open to suggestions.

Greetings

EDIT

Relevant code as requested:

if scanner == True:
    clocker.tick(clockspeed)
    if x < 11:
        slower = 3
        if firstTime == True:
            img.set_alpha(int(x * 25))
            newSurf.set_alpha(int(x * 25))
            screen.blit(newSurf,(xText,35))
            pygame.display.update((xText,35),((xText + newSurf.get_width()),(50 + newSurf.get_height())))
            img.set_alpha(255)

    elif x > (divider - 15):
        slower = 3
    else:
        slower = 0
        firstTime = False

    screen.blit(img, ((xStart - (x * increment) + slower),100))
    pygame.display.update(((xStart - (x * increment) + slower),100),(95,450))
    pygame.draw.rect(screen, (0,0,0), (((xStart - (x * increment) + slower),100),(95,450)))

      

        
        
        
      

    

The variable slower

should provide a sense of inertia as the boom reaches the far left and right sides of its sweep at a speed that it will slow down slightly.

The variable is firstTime

meant to fade in the panel when it first appears.

There is another loop just below this that is very similar, but views the image in reverse.