I’m not using PerfectDisk, no.

The reason i suspect Avast was doing it on its own was that Process Explorer showed large amounts of I/O and disk activity in the AvastSvc.exe process, but basically none in any other process. I think it’s unlikely that another program was accessing the files because it should have shown up as I/O or disk activity if they were. I can’t say it’s 100% certain, though.