Clutch chatter... cause and correction?

[jakeru]

Hey guys, I've owned my 2001 Boxster base for about a year now, and it's currently at about 110k miles. This is my first Porsche, and I've been getting a feel for what I like and dislike and what may not be working properly. (I did my own PPI). I've put on about 3k miles in the year since I've owned it using it as a daily driver.

The clutch has some chatter, but only in certain conditions. I think maybe heat related... when cold it chatters (can be pretty severe chatter), and when warmed up it can virtually completely go away so it feels like a perfectly normal clutch. Clutch has never had a problem with excessive slipping (which is to say, when the clutch pedal is released, it always "fully" grabs). Generally speaking, the chatter is only a problem when getting the car going from a stop. When shifting gears, it's not a problem.

By chatter, I mean the car pulsates or "bucks" a bit, when slipping the clutch. It seems if you feather the clutch enough and use light enough pressure, it won't chatter. It also seems using heavy pressure eliminates the chatter. So it seems there is a certain pressure range and temperature range where the clutch will chatter.

I replaced the front motor mount with a new 987-spec rubber insert, hoping it would fix the clutch chatter issue, but it did not seem to make any difference. (Old mount was cracked in places, but not completely separated.)

I've driven the car long enough that I don't think the issue will fix itself from "breaking in" (if the current clutch happened to be recently replaced by a previous owner).

I've got some service records from the previous owner going back to about 60k miles, but found no clutch work. (I suspect I may not have compete service records on the car, however.)

So my question is what is likely or possibly causing the chatter, and what do I need to do to fix it? If I pull the tranny from the engine to inspect, I'd like to have parts lined up that likely need replacement. Should I just have a new clutch disc+pressure plate ready to go, or should I instead (or additionally) have a new or good used dual mass flywheel ready to go?

Any other ideas or suggestions? Thanks!