Stationary off the bike I grab and hold the rear brake and drop the rear wheel there is a horrible noise. It’s created by movement in the pads I think. Any solutions to solving this noise as when I’m braking on rough terrain it sounds horrible.

Shimano pads or after market pads?

Does it make the same noise without the pads? Is it the rotor?

Try bending the spring so that it holds the pads securely and away from the disc.

They are after market pads.

I shall I have to try without and such tomorrow.