Strange sound

Hi guys just wondering if somebody could give me advice on where to look or what to do as i am a complete novice.





Lately i have to warm the car up for two mins or so before i set out, once the engine temp gauge needle has gone up a bit then its ok to drive.
If i start the car and then head out without warming the engine first, a few mins into the drive i get this strange grinding metal sound like two metal plates are connecting and the sound can vary but its like a rattle with the grinding sound to.
I had new belts put on months ago but not adjusted since, i get no screech sound on a very cold day when i start the car so the belts are all good, also the car has got newish pads and discs.
There is no effect on the handling or the within the car itself but to eliminate the sound i have to pull over and slow down with the brakes and just before i stop it suddenly dissapears and im free to carry on with the journey and theres is no more problems.
It is almost like i brake to pull over and then something realeases, like something is caught but is not.

sound like the rear brake shoes sticking on but why it doesn't happen when the car has warmed up I dont know

our jimny was only used a couple of times a month so if you parked it with the handbrake on then the rear shoes would stick to the drums and it would make a terrible grinding noise untill the brakes had been used a couple of times
it was probably with powerwashing it all off underneath before it was parked up for a couple of weeks between pay and plays

Its not a problem now we have discs on the back

Thank you for the reply it is much appreciated.
Should i just purhcase a set of new brake shoes or is there a way adjusting the shoes etc ?
I drive the Jimny everyday so it is only sat on the drive normaly at weekends for the Sat,Sun

For metal rattling, particularly heat related I would take a look at the catalytic converter heat shield to see if the weld have fractured