Problem with sub-woofer

[mdl23]

I purchased from a local electronics store a Sony HTIB in March of last year. Of course, in May (after warranty expiration) of this year I began having a problem. After 2 to 3 hours of continued use, the Woofer begins crackling and eventually all my speakers begin to crackle. Do I need to replace the speaker wire or is something wrong with the receiver? All Sony tells me to do is to mail the receiver to San Diego to take a look at it. Has anyone had this kind of problem? I will never buy a Sony product again.