I guess most Volvo owners have noticed the noise that comes from the ABS when the car first reaches 12 mph or 20 km/h after starting the engine, that is the ABS self check and it is normal. This is a "TTRRR" kind of noise that lasts for a fraction of a second (probably less than half a second).

On my 2006 S60 sometimes (has happened 5 times in the last 2 months) when the ABS runs the self check I get a very loud noise that lasts longer than normal.
I'll try to describe what it sounds like:
- it's like the normal self check noise amplified 10 times (it literally shakes the car)
- the frequency of the vibration is probably 4 times lower than the one of a normal ABS self check, it alsmost sounds like when trying to shift a manual transmission without depressing the clutch (mine is automatic though)
- it lasts for about 1 second (longer than normal)

I guess I could get the same sound if I recorded a normal ABS self check and played it back in slow motion.

Has anybody encountered the same issue? Any idea what causes this slow-down of the ABS check or why it is so loud? How much would it cost to replace it?

Thank you!