1998 Cadillac Concours bad ground?

Hi,
I'm getting this weird problem where, at any given time, when I click to open the doors to drive some where, I get no response or hear any lock opening sounds. So, I use my key, unlock. There are rumbling sounds being emited throuh the speaker system. I enyer the ignition key to start, my security system goes into operation with the horns blowing. Having gone through this many times, I've found that by removing the abd reconnecting the battery ground terminal cable, this seems to correct this and the engine and car's running returns to normal.
I have puuled all of the fuses, relays, in the engine compartment and trunk area and clean them, obviousley noting any that were blown. I have replacd th inadvert relay. I have cleaned both battery cables extensively. I have cleaned grounds I could get to. This car is one of three that is in rotation for use. I've pulled codes and found many in history and have noted their sources but none seems to point to this eratic starting problem. I am running out of things to check. Also, the radio stopped operating when this problem first started.
I"m about ready to donate her, but, she is a great winter daily driver.
Thanks,
ken
Severrna Park, Md