This is interesting, I started hearing a clicking/ticking/creaking noise from under my drivers seat a few weeks ago. it isn't loud enough to really notice with the windows down or music on, but it happens most often when just starting to accelerate from a stop. I'll get 2-3 "tick tick tick" noises from under my seat area. I've also heard it when braking or cornering. If I put my hand on the pieces of metal on the left side under the seat, I can feel a distinct "tick" or "click" vibration when the noise happens. I took it to the dealer and they said they didn't notice anything on a test drive. I have a manual, so either we aren't hearing the same noise, or you have been mis-diagnosed.

Have you tried tightening your seat/seat rails?

This.

Started the noise after a track day, so i'm not surprised. My clunk happens when I first sit down on the seat, and/or whenever I take a reasonably hard corner - the lateral weight shift coaxes a clunk that sounds like a hard tap to metal with a screwdriver.

Same as you, I can put my hand down and make contact with the rail, and I feel it, and gets stronger the further back I go. But I checked the bolts and they're all REALLY tight, and have NO play in them if I am next to the car and wiggle the seat. Though the wiggling does make the clunk, I don't see anything moving. I also feel a ping underneath the body of the car directly under the seat rail area when I wiggle the seat.

I am planning on diving in to check it out this weekend, when I can have more than 4 minutes to mess with it. Hoping I don't have to remove too much crap to find the culprit, but the bottom of the car ping makes me worry that something between the floor of the car and the underbody area broke hold and there isn't anything to tighten or something... We'll see. I'll report back if I find anything of interest.

Maybe the rail itself is damaged. They are just ball bearing slides. Perhaps the lateral forces of track day bent one

Perhaps. I got in there a bit last night, and found the more specific area that the issue is occuring. It is the rear left mounting point on the driver's door. I have tried removing the bolt with no luck. I tried once with a normal socket and lightly stripped it before realizing that it's supposed to be a E10. So I bought an E10 and it was too rounded off to bite. No luck. I then got out my extractor set (as a last resort) and still couldn't get it off - the extractor just destroyed the head.

Now I have to figure out how to get it out to really find the problem. If I rock the seat side to side, it'll still make the click, but if I jam my hand under to put more pressure on it it'll stop. SO It's some issue with that mounting bolt (that is now pretty badly damaged). Not sure if it's a damaged rail, or what. It seems so close to being tight and normal - like the wiggle room is less than 1mm, but it makes a harsh click when it does...

I'm not done investigating, but need more time to work on it than the 15min I had last night to fool with it.

I also need to source a new bolt before I remove this one now.

I have the same noise under the driver seat as well almost sounds like it comes from the rear sometimes too.

it might be either of these two issues. i thought mine was from the seat but ended up being from the rear

Axle issues - http://www.ft86club.com/forums/showthread.php?t=49511

Nut tightening - http://www.ft86club.com/forums/showthread.php?t=92971

I'm extremely glad it's neither of these...