Standard MY02 WRX.

On startup makes a fairly quiet but noticeable frrrrrr noise. If I engage the clutch and pull away immediately there is no such noise. Noise also occurs around 3000rpm.

May have started after the 60000 service (inc. cambelt change). Currently at about 62000 miles on original clutch.

Any ideas of diagnostics I can do (fairly good mechanically). Are there any places to check on the heatshields/covers for rattle, especially since the recent service? Do I take it to a dealer to be told that they will have to strip the engine to investigate