RB26s have noisy top ends, the inj and solid lifters see to that.
HKS turbos have HKS in raised lettering on the intake ie silver housing on the side facing the front of the car. if they were HKS turbos and were 'steel wheeled' that's unusual as they have steel wheels anyway, unless they were damaged. if the housing says garret it sounds like maybe they've just done a steel wheel coversion on the stockers.
did autotech suggest anything other than a turbo? i'd hope they could be more specific, or are they just as confused? try taking it to Trojan, John is a cluey guy.
don't worry too much, engines have all sorts of weird ass ways to make noises. have a look at your accessories, the ps pump can make bad noises when low on oil, and the a/c comp sounds like a meat grinder if it needs gas or it's bearings are shot.
also engine fan clutches make strange noises when they let go, alternatively see if the fan is hitting anything when it turns.