grinding

Hi Guy’s ..
I discovered a strange thing this morning I started the car and immediately put it in reverse.
As i was pulling out i notice a loud grinding noise coming from the back of the car, it sounded like something was stuck like a box or something.
I got out and checked to discover nothing.
I put in 1st and drive a little and still grinding like crazy.
After about 3 mins or so the grinding stopped.
Any suggestions?
Could it be a bit of moister on the rotors as it was morning?
Another? I want to disable the anti theft alarm can I do this by removing the fuse for the horn or can I remove the horn relay.
Thanx in advance .... 1985 325e

I resolved the grinding issue.
Some screws and springs fell off the handbrake and it was rattling around in there.