Tag,
Since as you said it is a wideband noise and no CDMA operators are present in your region.More likely than not, the external source of interference would be from an unknown source (eg. Illegal users etc) than a known source(Network operators), making it difficult to detect the source.
Please check the following in the vicinity of your site in question:
1) Any wideband repeater
2) Bad mast head amplifiers (If Any)
3) Earthing/ Sparking from any Electrical source.
Contact you local Telecommunication Spectrum Administrator for support, as they have the requisite equipment and powers to detect and regulate such source,