I noticed this issue has been reported in the past a lot, but it appears no one of the SoundCloud support team actually has been able to address the issue.
Ever since this week, SoundCloud API URLs are timing out followed by a 403 error when requested again.
For example, the following URL will return an empty page, and then a 403 error when refreshed: https://api.soundcloud.com/tracks/256202279?client_id=[CLIENT_ID]
This URL does work: https://api.soundcloud.com/tracks/256299992.json?client_id=[CLIENT_ID]
Update: As of 5/25/2016, the issue is still not fixed and SoundCloud has yet to reply with a satisfactory response.