I was so happy to have finally found this, I just had to share!
Ever since getting my V6 Spider, I've put up with an embarrassingly-loud creak from under the dash, which my TS Spider didn't have. Whenever I drove around a roundabout, a right-hand bend, into someone's drive, a service station, etc. CREEEEAK... it could also be induced by pulling up and down forcibly on the steering wheel. This made me confident that I could find the cause (being able to produce the noise with the car stationary).
To investigate, I removed the cover at the end of the dash (to check the fixing bolt beneath), then the steering wheel (I had to buy a puller to get that off), the column trims, fuses cover, and parts of the lower dash. I suspected the steering column bolts were loose. They weren't, but at least I'll now have chance to fix the non-self-cancelling indicators and the intermittent CODE aerial ring around the key.
You can benefit from all this - don't bother - I finally found the cause of the creak - it was simply a bolt under the rectangular plastic cover, in front of the instrument cluster, on top of the dash.
Easy to pop that cover off and expose two bolts - one, projecting forwards, secures the dash to the crossmember. This has a 10mm hex head and on my car, wasn't very tight. The other bolt was the important one. It projects downwards and secures the crossmember to the bodyshell - and that also wasn't very tight. It's also only a 10mm head (6mm thread) and that doesn't seem enough for such a structural role. It's quite hard to reach, being down a hole, and with the windscreen right beside it, I had to use a universal joint for my 3/8" ratchet and work very carefully to avoid the head of the ratchet handle pressing against the glass. Managed to tighten it at least half a turn and straightaway the creak was gone. It might be worth removing the bolt, putting some grease under the head, and some Loctite thread locker on the threads.
Therefore I'd recommend all Spider owners to pop those covers off and carefully check that those bolts are tight. Photo below shows the two bolts I'm talking about. Such an easy fix in the end...