I don't know how many klms you have done, but when i bought mine new in late 2004 the service log book stated to "check valve clearance and adjust if necessary", that was printed from the 1500 klm service onwards, they said that if i wanted that done it would be aprox $100 extra on top of normal service charge, they would not tell me either way if i needed it or not!
They wrote in my service book that "owner declined to adjust valve clearance as he stated not needed" ??
I have a mate who has been working as a mechanic at Mitsubishi for last 15 years, and a son in law who is a mechanic and they both told me that you do not need to adjust them as they are factory set, but some do slip thru that may need adjusting which normally shows up when engine warms up, hence the disclaimer in the service log book "adjust if necessary". I guess that means that if you don't elect to have it done and you run into trouble down the track then they might put it back on you for not "adjusting if necessary"
Its hard to say what the noise is without hearing it at the time, injector noise is a little different to valve noise, which can vary. I would suggest find another experienced mechanic to take it to when its warmed up and making the noise, the wobbly exhaust at idle is more than likely caused by a drop in idle towards stalling which could be any number of factors, but as your lancer is still virtually as new it should be running perfectly, mines done 165,000 Klms and it idles fine, no noise or vibrations, always ran 98 or 95 fuel from new, with injector clean in tank every 10K.