a mule-headed SOB... but I can't help believing this is Flash related.. I just don't know how.

Something to think about: Although I'm 90% sure you've tried all this by what you have posted.

Adobe Flash is notorious for lingering footprints. When installing the 'latest' MANY people have to completely uninstall and delete older versions or problems pop up. TOTAL DELETION I'm talking about here. You'd have to google it.

After the above... you MUST also delete all safari cache... then shut off ALL extensions and restart your computer. Check. If it works.. you've narrowed it down. It's either Adobe, (you should be good to go) or it's one of your extensions interfering. To find out "WHICH" extension, if that's the case, you'd have to turn one on at a time, restart, and check. Pain in the butt, I know.

If it's any consolation... I'm having an 'unsolvable' problem as well. On my iMac suddenly my fan will ramp up to full RPM's and CPU usage will max out... at which time my iMac is unusable. Happens daily. Apple can't fix it... my system checks out OK on all system diagnostics. It's probably some software application but finding it? Nearly impossible.. it doesn't show up in ACTIVITY MONITOR.

Actually I'm due for a new iMac.. OVERDUE in fact... BUT, and as you know... Apple has pretty much forgotten about computers and their attention is 100% on devices. MOST of their computers, laptops, desktops, are LONG overdue for upgrades.... the Mac Pro, for example... has been around for 4 years with NO UPGRADE AT ALL. iMacs not quite as back.. but WAY overdue.

"WHEN" they are going to update is unknown right now... so if I bought today sure as HELL they'd update tomorrow. I'm waiting them out - - could be a long wait. - JamesJM