Young Ball Python Feeding Concerns

[Squagem]

Good Evening All,

We purchased our beautiful ball python Koa back in November of last year, and until now he has be an absolute pleasure to feed! He usually immediately jumps at his mouse (now rat) and is done in a few minutes.

Recently, however, he has been rejecting his food quite frequently and I'm hoping to discover here what the underlying cause may be (as him regularly eating was previously the best way to determine his health). In order to help you all decipher what is going on, I'll provide some specific information on the situation:

• He is almost one year old;
• His recent feeding history is as follows:
  
  • 7/14/13
  • 8/12/13
  • 8/26/13 - Rejected
  • 9/02/13 - Rejected
  • 9/09/13 - Rejected
  
  
• His most recent shed was about 1.5 months ago (didn't write down date);
• His feeding area is quite large (4 square feet);
• We usually pre-scent his feeding area;
• The rat is no wider than the widest past of his body;
• I don't have a scale, but he feels like he weighs about 2.5-3.0 lbs (very inaccurate);
• His husbandry seems to be great (going to get another hygrometer tomorrow for the other side of his enclosure);
  
  • Heat gradient: 77 - 89 degrees Fahrenheit (in basking hide);
  • Humidity: Typically around 55%;
  • Substrate: Coconut fiber;
  • Security: 2 medium hides (small enough to fit snugly);
  • Light: One light on a timer (although it sits directly on top of the cage).
  
  
• We switched to feeding him rats in May;
• His vents are clean (no signs of illness);
• We usually feed him once a week (10:00pm on Sunday);
• He is typically very active at night when his light turns off.

I have attached a picture of both our little snake, and our enclosure (sorry for the low quality, the mass of light is his water dish).

I'm essentially hoping to hear some input on BP.net regarding what could be causing this behavior? Is it normal for a snake his age? Any assistance here would be greatly appreciated, as until now, we were so proud of ourselves as parents. We are definitely willing to take him to the vet if needed, however I don't want to incur a ~$300 fee if this is normal behavior. Thank you so much for your time, and I hope that all of your balls are doing wonderfully!