the comp wheel could be just starting to catch the housing, ive just done 2 turbos and one of them basically had stopped boosting altogether as the comp wheel was jamming in the housing due to excessive wear needed full rebuild kit shes all good now though the car commuts daily 60 miles.

it could well be the beginning of the end the noise but i dont understand you saying it feels flat yet you say it still spools the same and makes the same boost, if thats the case it cant feel any different due to the turbo, unless it is actually spooling later due to being so worn its starting to catch the housings. but your just not noticing the change in spool ?