Volvo S40 1.6 turbo diesel 2006.

Recently had all four callipers changed and also fairly recently had new discs and pads. Callipers we’re from eBay.
previously had an issue with rear calipers seizing.
The other day while driving I broke to a stop and it felt like I’d hit a bump in the road even though I knew I hadn’t, almost as if the brakes ‘bumped’ to a stop if you will.
Brakes are now making a slight grinding noise when braking. Not particularly loud but noticeable. no heat coming from alloys.

does anyone know what this could possibly be?

 

How about someone forgot to tighten one of the caliper retaining bolts? And now the caliper can touch the edge of the disc or the inside of a wheel.

 

Well your car being a diesel I assume you from UK , disks and pads wear out and are consumables , but calipers are not , certainly not on a 2006 model , does the car park outside in the UK constant drissle , so rust is a big problem? Grinding is never good but is you leave outside for a few weeks the disks rust up quite a bit so will grinde for a while , but should clear after a 20km drive
How many KM has tour car done ? , also sometimes a bit of grit gets in betweeh pad and disk , I dont think its loose calipers as you will hear the loud knock when braking and then the grinding will be all the time
I normaly change the pads , but to check them properly I take them out and a few times used a flat screwdriver whitch dets the pad a bit then for a little while dirt gets in which causes this grinding sound not good but clears after a few brake applications
In your case drive a bit like 50 km if the grinding does not go away you will have to check each calliper to see if a small stone etc is traped between pad and disk