I noticed recently that I get some turbo flutter if I give it some boost (5-10psi). This never, ever happens at WOT though. The car came with the Forge BPV, so could it need re-lubed? I'm sure it isn't anything major, but I just wanna know if it just needs re-lubed or something...

 

That's the first place I'd look. Mine starts to flutter juuust a little bit when cold if it's getting close to needing service.

If that isn't it bypass your vacuum tank and see if the BOV still does it, but my money's on a good cleaning and re-lube with some quality high temp grease. Don't over grease it and don't get any on the nose of it. Either make it stick sometimes.

 

Mine does it even whent its 80+ out. What grease do you use?

 

Well, I can say that did the trick! Cleaned it up, and put some Mobil 1 grease on it. It's also a little louder now and seems more responsive.

 

Mobil 1 synthetic is recommended; here's a link to proper method How to Service your Forge BPV - Mazdaspeed Forums.
You also might want to check if your valve has a green spring. They come with a green and a yellow; most have better luck with the lighter (green ) spring.

 

Yep, that's exactly what I used. It also did have the green spring as well. It didn't even take much to make it move smoother. I dabbed some on my finger and rubbed around the piston, without getting any on the tip. It has a nice even coat. I cycled it by hand a few times and it seemed smoother. And like I said, it's alot more responsive now and slightly louder.