Lower speaker sometimes work

Hi!

I have recently changed my sisters iPhone 5S (My old phone) to one of does fancy styling backplates to "iPhone 6 Mini" design. and after that the lower speaker only works a few seconds after reassembly...

When the screen is not pressed down in the housing the speaker works and several restarts, still working. After the screen is pressed into place the speaker still works but then later shorts out... Then the speaker works with the screen just been pressed down I can even restart it and then a little later the same thing...

I have tried taping the visible metal on top of the speaker with electrical tape but no luck..

Anyone had a similar problem?

Best Regards