Certain online maps freezing

So I bought Black Ops in November and had no problems. About 3 months ago, Villa and WMD maps froze up every time I played them online. Now, Berlin Wall, Villa, WMD, and Radiation freeze. It's very irritating. I have tried deleting all Black Ops files off of my PS3 and re-downloading everything. I've tried ventilating my PS3 more. I've tried moving my PS3 closer to my router. Nothing has worked. So, anything that can help me will be appreciated.

Other things:

My PS3 is a 40GB one from late 2009.
My Black Ops campaign audio started to stop a few weeks ago.
My disc isn't scratched.
None of my friends have this problem all of the time.

Thanks!