[Exhaust Making Wierd Noises?]

When I first start the car, every time I'm between about 2500RPM-3000RPM the exhaust makes kind of a 'whispering' noise.. can't think of a better word to describe it . Anyway, usually once I get to about 4th gear, it doesn't happen anymore and won't happen again until next time I start the car again

Does anyone know what might be going on? I have a feeling it might be because of that valve thing in the right exhaust pipe but that's just a wild guess cause I don't know what that thing does. I hope someone can help me out because it's pretty annoying

[What's This Thing?]

Thanks for your anwsers so far! I just thought i'd mention that the cord for the aerial comes out from behind the glove box and then splits into 2. 1 end goes into the back of my head unit and the other half goes into this box. So I assume that it is actually doing nothing at all because it isn't really connected to anything. Does that make sense?

[What's This Thing?]

Yeah, it's attached to the aerial cord and it has an aerial plug in it. I probably should've mentioned that. I just don't know what it's for and wether or not it needs to be there

[What's This Thing?]

Hi everyone,

Just last week I bought my first car, a 94 R33 GTS-4, but the guy sold it to me without a head unit in it. So I went and bought a new one and when I was putting it in, I noticed this little green box thats in the picture. Can anyone tell me what it is and what it does? I managed to wire everything up and it's all working perfectly, but I just found it strange that this thing is sitting there doing nothing. I don't know a thing about car stereos, so I'm sorry if this is a really dumb question