Haven't had time to follow up on all your suggestions but here's where I'm at:
Is this an older M-Audio 2496 card? Running on ASIO? Increase the buffer size.
Card is from 2008. It's running ASIO, sample rate 44.1kHz, buffer size 64. Haven't had a chance to try with larger buffer. I do notice that if I just play my piano on the thru channel but without the backing track playing, there's far less static than if I just play the backing track.
Otherwise please provide more info. What is your single-core Geekbench (free) score?
1835/4770
Does DPC Latency Checker (also free) show red spikes?
Haven't run it
How much free space by % is on your hard drive (more than 15, I hope)?
50%
Are all your audio and video drivers up to date?
Audiophile has latest updates, video driver I'm not sure.
You say it just started. What could have just changed such as a Windows update?
I checked the windows update log, it's all antivirus, MSE security stuff. The last non security update was .NET framework a week ago.