Fluctuating boost

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Hey
 
Iv noticed recently that my fc commanda is showing lower boost than usual, it used to show 0.8 but only showing 0.6 now.
I got my girl friend to watch the commanda while i was in boost and it fluctuates from 0.58 to 0.61.
The car feels like its pulling good but maybe not as well as it did,
Also at low speed i can here the turbos wistle a bit, sounds like it could be coming from the dump valve.
 
So i just wondered is fluctation normal? does the loss of boost sound like a leak? and can dump valves leak??
 
Could someone put my mind as ease please.