No rumbling but a clicking if I’m going round a roundabout. They seem to be really rubbing the discs?
Pads don't look worn enough to grind, take 'em apart and clean 'em up. As Snotts says maybe some grit stuck in there.
Looks a bit scored with road muck. I’d whip the pads out and clean them as a first step. Even when they’re fine, they may bind a bit until the rotating disc knocks them back a bit.
@Crispy seems to have the same front brake issues as you. See his caliper seals post. Your disks look badly scored and worn down with a rusted lip around the edge. Pads look good depth but surface looks bad and the caliper seal has issues. Sorry for repeating myself, but there comes a time with those all important brakes to renew them. If it were me, I would replace disks, calipers, pads and flexi hoses. All parts are readily available and if you don't want to fit them, you can source the parts and any decent garage can do the work, nothing complicated about them.
Seal kit, wire brush (face mask) clean it all up. I suspect the ker-nackered dust seals are preventing the pistons retracting after use. Re-assemble. Bleed the brakes. Good as.
The discs are fine. The lip is minimal and the scoring is pretty much non-existant. Think I’ll try and free off the pistons and bung it back together for next weekend; then get rebuild kits for the week after...