Lightroom :: Chromatic Noise Being Added To Photo When Exporting At Reduced Sizes

I have a preset in Lightroom set to export photos with the long-edge at 900px in length. Whenever I use the resize feature, the photos that result have horrible noise and I don't know what to do about it.  I can export the images at full size without any noise, then use Photoshop CS5 to resize the images and still have cleaner photos.
 
Here's an example.
 
The following export preset it set as such:

- Export as JPEG
- Quality = 100%
- DPI = 300
- Resize to 900px on long-edge
 
The first photo is exported via Lightroom 5 with the above settings, then directly uploaded to Imgur.
 
The second photo only has the Resize feature disabled in Lightroom.  It was then resized to 900px on long-edge in Photoshop CS5 and the uploaded to Imgur.
 
The only difference between these two photos is which program was used to shrink them down to 900 x 600px.
 
Here is link to the referenced photos: [URL]
 
 What do you think could be causing this? Since the only difference between the photos is which program resized them, all I can think is that it's an LR5 issue...