I have a 17 MBP unibody with the 2.8ghz Core2 duo and 4 gb of RAM and I have this constant lagging that is driving me crazy. I did a complete fresh install and still have the problem.

It's sporadic enough that it is sort of hard to describe, but here is a breakdown of the kind of things that are happening:

There are regular "pauses" in performance- e.g. QuickTime movies will have a stutter in picture every few seconds, iTunes will pause music every few seconds and Chome, Firefox and Safari all stutter when playing videos back in things like Youtube.

Also, little OS things lag a lot of the time, like right clicking to bring up the context menu will either be slow to respond or it will pop up but then not respond to the mouseover, closing instead. Also, simple things like typing in this window will occasionally pause for a second or two and then catch up.

Temperatures look fine and I don't notice any hits to the CPU or drives in Activity Monitor, and using Disk Utility to check the disk shows no problems.

One other potentially important note- the drive failed a month or two ago and I replaced it, and I do occasionally hear a click sound like the drive was asleep and woke up or something, so I am wondering if there is something causing the drives to go bad or if it is a coincidence. I think I was having this sort of problem before it failed, but I can't remember for sure. I replaced the drive with a non-apple drive (I think it was a Hitatchi) but it had the same stats- 5400 rpm and same cache, etc.

thanks for any help. Does anyone know of a great diagnostic tool or am I just best off going to an apple store?