Hashing speed dropped by 15%?

I have run into a problem where my hashing speed has dropped considerably. I'm currently running a brute force attack with the mask ?a?a?a?a?a?a?a?a. Usually my hashing speed sits at ~9500 MH/s, but it has dropped to ~8100 MH/s and I can't get it to return to the ~9500 MH/s it normally runs at. According to HWMon, the utilization still reads at ~97%-99%, which is normal, even though it's running at a slower hashing speed. However I noticed that the temperatures and fan speed are considerably lower than they were when it was running faster. Normally my temperature sits at ~73c and fan near 100% (while at ~9500 MH/s), but right now it's at ~64c and 34%. I'm not sure why they're different when GPU utilization is still nearly maxed. Does anyone know what has caused this drop?

I'm using a single GTX 970 with the latest drivers (372.54) to recover an NTLM hash using hashcat 3.00. I've 'checkpointed' it about 5 times while it's been running, but nothing should have changed with the hashcat command as I've restored its progress every-time. My progress is about 60% right now, and I think I started noticing the drop in speed at (very roughly) 50%. If you need any additional information let me know.

Some additional weird behavior I've noticed: When I launch a very basic 3D program that's probably mildly intensive on the GPU, the hashing speed jumps to ~9200 MH/s. The temperature also rises to ~80c, but the fan stays at 34%. If I launch a much more GPU intensive application, hashing speed drops to ~7600 MH/s with ~80c temperature and 34% fan. Not sure if this helps, but figured it wouldn't hurt including it.
Does your clock speed drop?