I have a strat wired with fender vintage noiseless pickups that was until recently working normally. However, I noticed a significant decrease in volume and output from the middle pickup, both my itself and when in combination with the bridge or neck pickups.

I popped open the guitar and looked inside. The wiring looks normal to me and I didn't notice anything that was out of order.

What could be causing the decrease in output? Is the pickup shot or is there a likely culprit I should check for in the wiring?
This might sound stupid but, have you adjusted the height of it at all?