I have a lot of experience with the Intel RAID but none with Linux. Substantially all of the RAID rebuilds or consistency checks I've experienced have come from unexpected shutdowns. We get these super brief power failures - sometimes not even long enough to flash the lights, but PCs not connected to an UPS will reboot as a result. We no longer have any PCs without UPSs for this reason, but that used to be a major cause of rebuilds.
That said, a failing drive could certainly be to blame. I'd at least monitor closely for a couple of weeks. I get good drive info from the Intel RST's SMART info and Intel Desktop Utilities - not sure if they have Linux versions. Also, the drive manufacturer probably has a diagnostic app you can download for free, again not sure about Linux but maybe there's a bootable version you can burn to a CD.