Its a straight forward job to remove the front timing cover to see if anything obvious is amiss.Timon said:
BTW, How does your mechanic know without removing parts what dollar value might be incurred... ? can he forcast how much I will win on the lottery.
Seriously though , if it does have Dinan cam gears, then it might be that the original Duplex chain was reused. It could just be the meshing frequency of the new gear sprocket to the more worn chain, or the holes in the camgears moving air at certain rpm causing an airborne whistle.
My bet is that there is nothing wrong but an inspection would not hurt.
Regards
Farrell