I would not hesitate in taking it in
You cant be sure enough with those sort of noises - and if it is the brake booster, I 'aint heard it before - so maybe mine is broke?!!!???

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2008 E70 4.8i M Sport, Aero Package, Saphire Black on Black
215 21" wheels, Comfort Seats, Active Headrests, Sunroof, Premium Sound, Einsenmann Exhaust
Inbound: ACS Interior, Carbon Roundels and DVD System.

2005 E53 X5 4.8is (donated to wife)
2007 E90 323i M Sports Tourer (retired)
2006 E46 M3 Cabriolet (retired)
2001 E53 X5 4.4i Sports (retired)