Hissing Sound?

Thanks all for the advice. I actually learned a lot about a few other things I need to do anyway like the clutch adjustment. Turns out it was a hose that came loose under the aircleaner. I'm not sure what that's called that it's attached to, but I stopped for gas this morning and finally had daylight to sniff around in there. Found the house detached, reattached it, and presto, hissing stopped. Can anyone tell me what the hoses do that go into and out of the aircleaner? I know that's a "stupid" question, but I've been trying to figure that one out.