air filter flutter

[redSRpilot]

this is my first post and i know this topic has been brought up before but i still cant find an answer. i have a 91 240sx with redtop sr20det. i am getting fluttering in my air filter, and am trying to find a way to fix it. i have read post after post after post,( for those of you that are just going to tell me to search more ) and there seems to be a lot of different reasons for it. also, my bov is not opening and if i loosen the adjusting screw any more air is let out at idle. at idle my vacuum is 21 in/hg, and then gets less and less as i accelerate and then goes into boost. at cruise its at 10-11 in/hg. is that normal? im not sure if thats too low at cruise, and is causing my bov not to open. a bov is a pretty simple thing, so i dont understand how it could be bad? i think all my vacuum lines are set up properly, but maybe not if my vacuum isnt how its suppose to be. some ppl say my turbo might be blown, but i dont have any shaft play, and no smoke coming out my exhaust except for the black smoke because its running rich. im out of ideas so if anyone knows of something i can check or has any answers, it would be veryy helpful.