rattle when i start / clutch squeal

[HijackTheLeft]

When I first start my car, it makes a disgusting rattling sound... its hard to pinpoint where exactly it's coming from, but it sounds like somewhere in the exhaust. It only lasts for maybe 2 seconds, and then it goes away. Also, until my car warms up, my exhaust sounds terrible. I've been told I may need to replace the catalytic converter, but I wanted to get Nico's opinions first. I'm assuming these problems are related...

also, when i'm in neutral there's a slight squealing sound similar to a slipping belt. pushing the clutch in maybe 1/2" gets rid of the sound, but does anybody have any idea what might be causing it? I'm not sure exactly when it started. I changed the clutch about a year ago. I've taken it to the track a couple times, once to the dragstrip, and one autocross. I usually don't drive hard on the street, and the times at the track, I didn't really push the car too hard, because its my daily driver. I don't know if that's relevant or not, but I figured I'd mention it.

Btw, i have a 90 s13 with an intake, and everything from the headers back is aftermarket, but i dont know exactly how old it is since ive had the car for about 18 months and it was all on there when i got it. theres a few other mods, but nothing that really pertains to these questions...

thanks in advance!!!

EDIT: Now that I live in florida, i don't think theres any emissions regulations... or so i'm told. what are the pros/cons of welding a straight pipe in instead of putting a new cat in??

[HijackTheLeft]

...bump... ?

[ChoyLiFut240]

You might want to check you master cylinder. I have the same problem where it makes the squealing right when it starts until I take out the clutch. Sometimes for my car it makes the squeal whenever I put the clutch in and right when I take it out the squeal goes away. I just recently found out my starter is going out cause it's getting old and I know the starter affects the that area of the car. I'm not sure if the starter would be the problem for your car but hey I'm just throwing any idea out there.