No physical clunking noise, but there is an overall sluggishness to my Mac. Apps are slow to open, mouse slow to respond, dock sometimes freezes. I have a fiber optic internet connection with regular 5 meg down and 2 meg up speeds (as tested on Speakeasy) and video played online is clunky, maybe 10 frames a second, even after the video is fully loaded. DVDs play fine. Both Safari and Firefox take 30 seconds or more to open seemingly simple pages. The Activity Monitor is regularly maxed out. I have about 24 gig of free space and I store most of my stuff on a 500 gig external drive which I got due to the slowness experienced, thinking that would solve the issue, but it didn't. There is 24.5 gigs of free space on the internal hard drive. I have no 3rd party software loaded and no extra Apple hardware loaded. The machine is about 8 years old. Any ideas where I can look to figure out how to get the old speed back? It's running 10.11.4 with updated Firefox and Safari. If I'm in the wrong forum, please suggest where I can post this. Thanks!