A few weeks ago I took off from my house with some SWAG so to speak and noticed a chattering/frapping sound coming from the engine right around 4500 rpm and up. The sound seems to be located directly in front of the drivers position and the sound is only noticeable under boost... Now it was roughly 35 degrees out, I can gently get the car up to 6k without boosting and I do not hear the noise, but once I open full throttle... the "frapping" begins. I can also hear the noise while revving the engine in neutral... once I hit 5k or so the boost needle moves ever so slightly and I can hear the noise as well. I'm pretty sure it has something to do with the sound symposer... It almost sounds like a rattling near the cowl top, but the fact that I only hear it when boost kicks in makes me lean towards the symposer. Now a few weeks ago when it was like 5 degrees and lower... I did not hear the sound. I'm thinking of pulling the tubing for the symposer where it connects to the firewall and seeing if the noise goes away. If so. I'm just going to bypass the symposer regulator and go with it on all the time. If any of you have experienced any odd sounds as well, please let me know!!! Thanks!!!!