After swapping my front tyre and putting in some new brake pads, my bike developed an issue.

When I am braking I get the usual squeal at lower speed, but when I'm getting close to coming to a stop, there's this terrible grungy noise that I can only liken to the sound a lot of semi trucks make when braking and coming to a stop.

Accompanying that sound is a really weird vibrating feel in the handlebars.

I tried to search for this exact issue but didn't see it.

I don't get anything like grab/release issues or constant vibration like you would from warped rotors.

I would note that when just rolling the bike around, there seems to be significant contact from the pads (not as easy to push around as the gsxr or triumph).

Any ideas?

I suggest remove and replace with a good cleaning of the calipers prior to installation of the pads. It could not hurt anything to get a new close up visual.

did you clean the pistons and check the o rings when you replaced the pads?

Have you checked that the pads are seated properly and the clips are Ok ie not being held at a strange angle by things not seated properly?

Give the discs a good clean, some pads can leave a coating on the disc that may be affecting your new ones.

It seems I fooked up by not doing any cleaning prior to replacement.

Pads are seated properly.

Did not check O-rings.

Brakes (at the caliper) are not something I've learned to mess with yet

You could have a bent rotor, if you have a die grinder handy you can get some buffing pads and clean up any rough spots you feel.