Logo placed in InDesign loses transparency only when exported to PDF

Hi,

I'm having trouble with the background of a logo remaining transparent when I export the InDesign file to PDF. I've placed (cmd D) the logo into the file and the logo is transparent while editing in InDesign, but when exported a faint background box appears. I've attached screenshots of the edges of the logo to try and explain this.

The edge of the logo while in InDesign:

The edge of the logo when exported to PDF:

My original file was a transparent PNG 24 file, but I've also tried replacing the logo with .psd files, .ai files and .tiff, but the same problem keeps occurring.

Thanks in advance for the help!