Most prominent at 2000 rpm if i hold the throttle but i have a ticking tapping noise which sounds like it's coming from the left hand side of the engine looking at the car, can be heard up to 5000 rpm also.
Had this in an m3 but got better after valve shim adjustment and it's only really annoying when coming through the town with the window down then it's easily heard.

Been reading up on it and can be quite normal?

Could be up pipe gasket, noisy injectors etc

What kind of lifters does the type uk sti engine run?

Just doing my head in a bit but car pulls hard and runs great at 97,000 and ppp

 

Could well be uppipe gasket,you should be able to feel any exhaust gasses escaping,injectors can be noisy but doubt you would hear them from outside the car with the bonnet shut.
You will have solid bucket lifters with fixed under bucket shims.
What grade oil are you using? If your going to the manual which i believe says 5w30 then this might be a little thin for a 100k miles car,you could try a slightly heavier oil,this sometimes help with tappet noise.

 

Yeah might just get the gaskets changed but will be a nightmare with all the rusted heat shield bolts.
Thanks for the info on the lifters, and have just changed the oil to 15w 50 fuchs race r, done around 300 miles since

 

Have a look under the car it could be any of the exhaust gaskets,manifold is an easy one to check,you should see signs of a blowing exhaust,black soot around the joints.
Maybe worth checking spark plugs too as a loose plug can cause a ticking noise.

 

Had this on my classic, it slowly got louder and in the end it turned out to be spark plug that had worked its way loose.

 

Does it increase in frequency in concert with revs rising?

If so, more than likely to be any of the exhaust or up-pipe gaskets.

However, it could also be the beginning of a failure at the collector area of the exh. manifolds. I had this on an aftermarket equal-length Syms item. It gradually got louder as the hole got bigger, and ended up sounding like a ruddy tank or tractor lol.

 

Yes the tick speeds up with revs

 

I've just had a reciprocating tick/rattle in that rev range sorted by changing the clutch, which was a nice side effect.

 

Could be loose spark plugs i have a vid of my car on facebook when it made the noise check if yours is the same

I had no obvious negative effects other than a noise

 

ill start a new thread with a video link, just done one