It'll pretty hard to diagnose a noise over the forum without hearing it. But if you're gonna try, give us more info. You already mentioned it doesn't matter if you open the throttle fast or slow. Does it happen at a certain RPM range? Is it only above/below a certain RPM range? Does it happen in all the gears, or only in certain gears? Noise still there in neutral? Is it truly a "vacuum leak" type of whistle, or like others mentioned more of a gear sound coming from the engine? Seeing how dirty that filter was, how is the oil? The 675 likes to be FULL, and the dipsticks even changed in 2009 to move the min/max marks up. On a 2007 you're safe running it about a 1/4" above the max mark, in fact I'd recommend it. The valvetrain on these bikes can make a lot of noise, especially if your cam chain is a little worn (put a manual tensioner on there, the 2006-2008 spring-loaded ones suck) or the valve clearances are out. Let me know what's up. If you're taking it to Pauly for 24k service I'm sure he'll check the valves and might be able to get you squared away. And my offer still stands if you want me to take a look at it. I've worked on more than my fair share of 675's and know a lot of the common issues with them.