Odd noise from footwell

[me-tm]

I'm getting a strange noise from the driver's footwell.

It only happens about 2/3rds of the time when I either lift off the throttle sharply or depress the clutch quickly. The sound is quite a sharp TICK rather than a clunking I'd usually associate with something big like an engine / exhaust mount. It sounds more like somebody hitting the bulkhead with a screwdriver.
If I open the window I can hear it from outside too, suggesting it's in the engine bay.
I thought I'd traced it earlier when I found out my throttle pedal had about an inch of lateral movement :oops: Tightening that up didn't fix it though.

Any ideas?

If you're too lazy to look over to the left, just below my avatar, the car is a '97 Ph1 XLdt.