I've been having a few issues as the temperature has been dropping recently...Most notably is my blow off valve hasn't been completely opening under certain conditions. Driving around town its most noticeable, if I reach between 0-5 psi and let off the gas or shift it used to open, now I get a harsh fluttering sound and the car sort of bucks a little with it. 5+ psi, it opens but it just sounds different then it has before. And driving at -10 psi, I can sometimes hear it whistling a little..I have a greddy type s with the single spring mod, recirculated and I've never had a problem with it last winter or all summer. It was installed by the previous (original) owner presumably years ago.
Next problem I'm having is backfiring. It seems to be connected with when the blow off valve doesn't open all the way, but I've never noticed any backfire before. It's not loud, but it's never happened before that I've noticed.
Another problem I've encountered is an odd squeal in the front when coasting in neutral. It's not the standard tcase whine, but it sounds like that's where its coming from. It seems to only happen from 30-10 mph and stops below 10mph, and it's hard to describe the sound and it doesn't happen every time...might be a long shot with no one being able to hear it in person but I figured I'd mention it see if I could get some help. I know the fluid needs to be changed.
Overall, the car just seems off...not running like it used to. It is due for an oil change, but I doubt this would be the root of my problems. It's been 3k miles (but almost 6 months!) since I last changed it...any ideas?

 

Check the bov vacuum source for leaks. Do a boost leak test. Pull the bov and push on the diaphragm and see if you can move it with your thumb, it should be pretty smooth. My friend had and issue similar to this with his turbosmart, he used a silicone lubricant and it worked well.

It backfires between shifts? check the plugs, and maybe because it's really rich because the air is not circulating back through?

Hit me up sometime man. There was a huge meet tonight but i can't make it I'm stuck at work :/