Dropbox high CPU, WRSA issue?

In the past week or so I've experienced Dropbox constant CPU of 25% or more when not syncng files, but even at that level the PC grinds almost to a halt. The PC starts OK but after about an hour it progressively grinds to a halt over the next hour, weird. I've done all the usual troubleshooting, re-installing Dropbox, clearing our rubbish, registery check, checks with 4 other scanners.
 
I'm at a loss...until I removed Webroot as part of the troubleshooting, now it's back to normal! I checked to see if WRSA was monitoring dropbox, but it wasn't, all seemed to be OK according to the control panels.
 
Anyone else experience this? I recall reading recently that WRSA had apparently been self-deleting Dropbox files with one or more users, but I've checked and nothing appears to have disappeared.
 
For the moment I'm purring along with WD until I can understand what happened and be confident that I won't end up having to troubleshoot for lots more valuable hours.