More than likely a clutch problem, but....HELP

I'm hoping for this to not be the clutch, seeing as how I just paid $400 for a custom clutch job from a friend about 4 months ago. But after testing out the problem and looking for the origin of it, I can't help but assume it's the clutch.

So for the past month, I've noticed an odd rattling sound coming from under the car, whether I'm driving or not. Now, that's not to say it ALWAYS happens when I'm driving, because it only seems to be when the car is not in gear, and the clutch is not engaged.

I can be sitting at an idle, hearing the noise fairly loud enough to where I don't need to lean in or get closer to hear it. The noise promptly disappears when the clutch is engaged and becomes non-existent. Knowing this, I think it's safe for me to assume it's again the clutch, but I'd rather have a discussion with a few people before I go blow more money.

I was reading that it could possible be the gear box (?) or something like that, but I'm not 100% that's how the system even works.

If ANYONE could help me out, I would GREATLY appreciate it, looking to fix up the car and make it reliable before I go throw modding money at it lol..

HALP
:ugh:

More than likely a clutch problem, but....HELP