Guys,
I have a classic sti, when I first start her up she sounds like a knackered trany van ! You don't really notice the noise on tick over, but at 2-3K revs it is very noticable. After a few miles or 3 or 4 minutes the noise goes away ? I have not noticed any performance or running issues apart from the noise ? Sounds like it could be the valves ? any ideas ?

cheers

 

It could also be piston slap - your description fits the symptoms very well!
Piston slap is most noticable when accelerating fairly gently through the rev range you describe and as you say, it goes away as the engine warms. It needs diagnosis by a Scoob specialist to confirm.
JohnD

 

This is common for scooby's isn't it ? I thought it might be that ? Thats when the piston is cold and not a really tight fit until it has warmed up enough ? Does it actually do damage ?

 

most cars live with it for a long time

when its noisey and its warm, that would be the time to get it looked at


i would just put up with it and enjoy the car

 

Piston slap in itself need not be damaging although the reason for it appearing is worth investigating. Gentle, off boost driving until it goes is the thing to do.
There was a problem with some (quite a few actually!) late phase one engines - '97/'98 WRX and UK I'm not too sure about STi's though, as these had forged pistons as opposed to cast items in the "lesser" version. Lots of people on here have first hand knowledge of the problem, so I'm sure you'll get more information. I certainly recommend you get it listened to though.
JohnD