This is a SEAT ibiza MK3 (6L) with FSIII brake calipers mounted (Factory VW).
The car makes an annoying rattling sound over bumps and bad asphalt since I bought it a year ago and I've finally found the problem, the front brake caliper is loose and doesn't contact the brake carrier like it should, I've confirmed the issues by applying the brakes when driving and the noise stops. This car has the FSIII brakes.
I found that there was slight play in the caliper, enough to cause the brake pad and caliper to bang against the carrier with every jostle and bump. The caliper should only be moving in and out along the sliding pins, but since there is a soft bushing around the pins it kind of pivots slightly up and down allowing a tiny bit of movement between the caliper and carrier which makes a huge racket when driving. All parts are genuine VW parts as the car was serviced at a dealership when the brakes were changed last.
My initial thoughts were worn out or loose pins and bushing, but upon closer inspection the pins where correctly torqued (28 Nm) and they were in immaculate condition with no rust or gouging on the surface, they also had a very tight fit (almost interference) inside the bushing with no play so I doubt that's the problem. The official SEAT (VW) repair manual makes no mention of any lubricant whatsoever, neither on the sliding pins or the sliding surfaces of the brake pads, only a thorough cleaning and rust removal. The brake pads also fit snugly on the caliper with no movement so springs seem to be intact.
Are these calipers designed to wiggle around a little? Any suggestions to fix the noise?